Required Reading SWGIT Documents - Scientific Working Group on imaging Technology (SWGIT) Sections 1-3, 5, 6, 11 and Guidelines for Developing SOP s and Training in Imaging Technologies.* Almond v. The State http://www.lawskills.com/case/ga/id/99/ Kennedy v. State of Florida http://www.fdiai.org/articles/dig%20imagin%20flpd.htm Iowa I.A.I Newsletter, State v. Hayden, Wash CtApp, DivI, 2/17/98 http://www.geocities.com/cfpdlab/perspect.htm State v. Hayden, 90 Wn. App.100, No. 38162-8-1. Division One. Feb 17, 1998* State of Florida v. Reyes, Circuit Court of the 17 th Judicial District, Case: 99-11535CF10A.* Berg, Erik C., Legal Ramifications of Digital Imaging in Law Enforcement, Forensic Science Communications, October 2000, Volume 2, Number 4 http://www.fbi.gov/hq/lab/fsc/backissu/oct2000/berg.htm McCoy, John, Digital Photography and the Risk of Manipulated Evidence, CHAR Patterns, Newsletter of the Wisconsin Chapter of the IAAI, April 2005.* (Note: This article is include in the reading list for this program with the permission of the Wisconsin Chapter of IAAI and the author) Section 15.2.3.4, NFPA 921, Guide for Fire and Explosion Investigations, 2004 Edition. Digital Photography and the Fire Investigator 1 CFITrainer.net
Additional Reading To review all of the Scientific Working Group on Imaging Technology (SWGIT) Documents see: http://www.theiai.org/swgit/ Hodges, Keith, Admissibility of Still, Digital Photographs (images) in Criminal Trials http://www.khodges.com/digitalphoto/ Shaw, Christina, J.D., Admissibility of Digital Photographic Evidence: Should it be Any Different Than Traditional Photography? http://www.ndaaapri.org/publications/newsletters/update_volume_15_number_10_2002.html United Kingdom Digital Imaging Procedure http://www.crimereduction.gov.uk/cctvminisite23.htm Litwiller, Dave, CCD vs. CMOS: Facts and Fiction, Photonics Spectra, January 2001. http://www.dalsa.com/shared/content/photonics_spectra_ccdvscmos_litwiller.pdf Janesick, James, Dueling Detectors, OE Magazine, February 2002. http://www.dalsa.com/shared/content/oe_magazine_dueling_detectors_janesick.pdf NOTE: Materials identified with a (*) are included in this document. Other materials should be downloaded from the listed site by the participant. Digital Photography and the Fire Investigator 2 CFITrainer.net
Common Terms These common terms are used in the presentation but may not be fully explained in the program or available reference documents. Other terms or acronyms used are discussed in some detail in the supplemental materials provided with this module. CCD (charged-coupled device) The original type of device used capture digital images dating back to the 1960s. Used in early digital cameras and many other imaging devices. The CCD image sensor is pixilated and captures the light from the image. The sensor converts the light to an electrical charge that is then transferred to a component in the device that converts the charge to voltage. The voltage for each pixel is buffered and sent from the chip to a printed circuit board located in the camera. With CCD technology most of the functions take place on the camera s printed circuit board rather than on the imaging device. CMOS (complementary metal-oxide semiconductor) Like the CCD, the newer CMOS device is pixilated and captures the light from the image. The conversion from charge to voltage takes place in each pixel and most functions are performed within the CMOS chip rather than on an external printed circuit board. The CMOS technology is faster and requires less power to perform its functions. Many of the newer high resolution digital cameras on the market today use this technology. ISO (International Standards Organization) A numeric indication of the light sensitivity of a digital cameras imaging device. The higher the ISO speed the greater the sensitivity to light. This number correlates to the ISO rating of film used in conventional cameras. In digital photography high ISO speeds result in the introduction of digital noise on an image. Typical ISO ranges for prosumer and professional digital cameras will be from 100 to 1600 or greater. Digital Photography and the Fire Investigator 3 CFITrainer.net
SWGIT DOCUMENTS The Scientific Working Group on Imaging Technology (SWGIT), was created to provide leadership to the law enforcement community by developing guidelines for good practices for the use of imaging technologies within the criminal justice system. A goal of the SWGIT is to engage the entire law enforcement imaging community in the development of these guidelines. Please review these documents carefully and let us have your feedback (Instructions for sending feedback). Thank you for your consideration. Sincerely, Richard W. Vorder Bruegge Chair, SWGIT
Version 2.3 2002.06.06 Background Section 1 Guidelines for the use of Imaging Technologies in the Criminal Justice System **Released previously as Definitions and Guidelines for the Use of Imaging Technologies in the Criminal Justice System ** Although digital imaging technologies have been used in a variety of scientific fields for decades, their application in the criminal justice system has been relatively recent. Consequently, there has been a need to gather and disseminate accurate information regarding the proper application of this and other imaging technologies (including silver-based film and video) in the criminal justice system. Mission Statement The mission of the Scientific Working Group on Imaging Technologies (SWGIT) is to facilitate the integration of imaging technologies and systems within the criminal justice system (CJS) by providing definitions and recommendations for the capture, storage, processing, analysis, transmission, and output of images. SWGIT Membership The Scientific Working Group on Imaging Technologies (SWGIT) consists of over thirty photographers, scientists, instructors, and managers from more than two dozen federal, state, and local law enforcement agencies, as well as from the academic and research communities. All SWGIT documents represent the consensus opinion of this membership and should not be construed as the official policy of any of the represented agencies. Purpose of this document This document is intended to serve two purposes: 1) Provide definitions for use by personnel in the criminal justice system when discussing imaging and imaging technologies. 2) Provide preliminary general guidelines for use by personnel in the criminal justice system as they develop specific standard operating procedures for their respective agencies. Future documents will address other topics in the field of forensic imaging. Part I: Guidelines Documented Procedures Personnel engaged in the capture, storage, processing, analysis, transmission, or output of imagery in the criminal justice system should ensure that their use of images and imaging technologies are governed by documented policies and procedures. SWGIT Guidelines for the Forensic Imaging Practitioner 1
Preserving Original Storage The original image should be stored and maintained in an unaltered state. This includes maintaining original digital images in their native file format. Duplicates or copies should be used for working images when applicable (see Post-Capture Processing). The following media are recommended for the preservation of original images because of their quality, durability, permanence, reliability, and ease with which copies may be generated: Silver-based film negatives in 35-mm or larger format Write-once Compact Disk Recordable (CD-R) Digital Versatile Disk Recordable (DVD-R) The following are acceptable for the preservation of original images but care must be taken to avoid loss of data: Photographic prints including prints produced through instant photography (Users are cautioned that individual photographic prints do not usually contain the full resolution and dynamic range available in original film negatives) Diskettes Magnetic tape Fixed hard drives Removable magnetic media Compact flash cards PC cards Smart media Removable magneto-optical drives Write-once magneto-optical drives The following are not considered to be acceptable for the preservation of original images: Inkjet prints Solid ink prints Thermal wax paper prints 2 Guidelines for the use of Imaging Technologies in the Criminal Justice System
Version 2.3 2002.06.06 Dye-sublimation prints Dry-silver prints Laser prints Electro-static prints Preserving Original: Post-Capture Processing Film: Can process the original if the processing is non-destructive. Analog Video: Recommend minimal processing of original to avoid degradation of signal. If original is used, a copy should be made prior to processing and analysis. Digital: Make a duplicate image and use the duplicate as the working image. Documentation of Image Processing Techniques common to traditional darkrooms and digital imaging stations, such as cropping, dodging, burning, color balancing, and contrast adjustment that are used to achieve an accurate recording of an event or object, are standard processing steps. When the results of these steps are visually verifiable, documentation of such steps is not considered mandatory except when the image is subjected to image analysis. Techniques, such as unsharp masking, multi-image averaging or integration, and Fourier analysis, that are used to increase the visibility of specific details in an image at the expense of other image details are standard processing steps. However, the use of such steps should be documented in the case notes in sufficient detail that comparably trained personnel can repeat the steps and produce the same output when the image is subjected to image analysis. (See "Recommendations and Guidelines for the use of Digital Image Processing in the Criminal Justice System"). Verification of Original and Processed Images Personnel who captured the original image or were present at the time the original image was captured can verify that the image is a true and accurate representation. Any processed image subjected to image analysis should be documented with an image processing log. An image not subjected to image analysis does not need a log. It is recommended that the image processing log document steps such as: dodging, burning, color balancing, contrast adjustment, unsharp masking, multi-image averaging or integration, and Fourier analysis. The use of such steps should be documented in the case notes in sufficient detail that comparably trained personnel can repeat the steps and produce similar output. Preserving Images: Chain of Custody Agencies must develop chain of custody policies for archiving images. For digital images, the chain of custody should document the identity of the individuals who had custody and control of each primary digital image file from the point of capture to the creation of the archive image. Once the file has been archived, the chain of custody should document the identity of the individuals who had custody and control SWGIT Guidelines for the Forensic Imaging Practitioner 3
of custody should document the identity of the individuals who had custody and control of the archive image. Guidelines for Software Software used in the processing and analysis of digital images should produce consistent results, permitting comparably trained personnel to achieve similar results. LEGAL NOTE: Manufacturers of software used for image processing may be required to make the software source code available to litigants, subject to an appropriate protective order designed to protect the manufacturer=s proprietary interests. Failure on the part of the manufacturer to provide this information to litigants could result in the exclusion of imaging evidence in court proceedings. This should be considered when selecting software. Guidelines for Image Compression Original images and images expected to undergo image analysis should not be subjected to lossy compression. If compression is necessary, lossless compression is strongly recommended. If lossy compression must be used, then the highest quality option is recommended. Note that if lossy compression is used, critical image information could be lost and unwanted artifacts introduced as a result of the compression process. Repeated saving of a file using lossy compression may exacerbate the loss of image information. Guidelines for Image Capture Image capture devices should be capable of rendering an accurate representation of the item or items of interest. Different applications will dictate different standards of accuracy. At a minimum, the following should be considered when selecting appropriate devices: Characteristics (size, movement, location, etc.) of the scene, item, or items of interest Lighting of the items of interest Dynamic range of the scene Time constraints Required end product(s) When documenting major crime scenes it is strongly recommended that a camera capable of manual override, with interchangeable lenses, off-camera flash, and a tripod mount be used as the primary capture device. Conventional silver-based film in 35-mm format or larger is recommended for use as the primary media in this case. This documentation may be supplemented by video and/or digital still imaging. It should be recognized that some agencies may wish to utilize equipment other than that recommended above. In such circumstances, the agencies should demonstrate and document that the selected equipment is adequate to meet the agency's anticipated needs. 4 Guidelines for the use of Imaging Technologies in the Criminal Justice System
Version 2.3 2002.06.06 Further information and additional SWGIT recommendations relating to different law enforcement field applications may be found in the SWGIT document "Guidelines for Field Applications of Imaging Technologies in the Criminal Justice System". Further information and additional SWGIT recommendations regarding image capture devices for Forensic Laboratory applications are not yet available. Guidelines for Image Output An output device should be capable of producing an accurate representation of the input image. The following should be considered in the selection of output devices: Final use of image Time constraints Longevity/permanence of output image Spatial resolution required Range of colors and brightness to be produced Guidelines for Image Transmission Received images should accurately reflect the transmitted images. The following should be considered in the selection of transmission methods and devices: Final use of image Time constraints File size Security of transmission Integrity of transmission Hardware and software compatibility of transmitters and receivers File format compatibility Part II: Elements of Standard Operating Procedures (SOPs) The following should be considered when formulating standard operating procedures: Title: The title should be a descriptive name for the procedure. Purpose: Why, when, and by whom the procedure is used. Equipment/Materials/Standards/Controls: Identifies what items are required to perform the procedure. This may include protective equipment, hardware, software, and configurations. SWGIT Guidelines for the Forensic Imaging Practitioner 5
Procedures: A step-by-step description of how the procedure is conducted. If appropriate, instructions should include precautions to be taken to minimize degradation. Calibration: Describes any steps required to ensure the accuracy and reliability of the procedure. Where applicable, instrumentation setup and calibration procedures should be documented. Calculation: Describes any mathematical operations that are applicable to the procedure. Limitations: Describes any actions, interpretations, or equipment that are not appropriate for the procedure. Safety: Identifies and addresses potential hazards in the use of the procedure. References: Identifies documents both internal and external to the user agency regarding the procedure, related procedures, and principles behind them. Part III: Quality Assurance Personnel utilizing images and imaging technologies in the criminal justice system should implement quality assurance programs to ensure that results achieved are repeatable and valid. As part of these programs, performance checks and corrective actions should be documented. Equipment Where applicable, equipment utilized in imaging should be checked regularly for proper performance and calibration, and findings documented. Where applicable, an end-toend system check for consistency within specified system parameters should be performed on a regular basis and whenever modifications are made to the system. All equipment should be maintained according to the manufacturers= specifications and recommendations as contained in the operating manuals. When a piece of equipment or a system falls outside the specifications and recommendations, the equipment or system should be taken out of service until it has been corrected. Evaluation of equipment and system checks should be documented inclusive of corrective actions. Software If software errors that significantly affect the results of a processing step are detected, then corrective actions should be taken. If the manufacturer identifies software errors and provides corrective remedies for them, the remedies should be implemented before the software is used again. Once corrective actions have been taken, an end-to-end system check should be performed prior to putting the system back into operation. Personnel All personnel utilizing imaging technologies shall be trained and tested for competency and proficiency in the agency=s standard operating procedures and the operation of the relevant imaging technologies. A formal training program should be documented and maintained, with the results of competency and proficiency tests documented. 6 Guidelines for the use of Imaging Technologies in the Criminal Justice System
Version 2.3 2002.06.06 maintained, with the results of competency and proficiency tests documented. Proficiency testing should be repeated on a regular basis or when significant changes in hardware or software are made. Part IV: Training Issues relating to training in imaging technology are addressed in the SWGIT document "Guidelines and Recommendations for Training in Imaging Technologies in the Criminal Justice System". SWGIT Guidelines for the Forensic Imaging Practitioner 7
Version 1.2 2001.12.06 Section 2 Consideration For Managers Introduction This document provides managers with considerations generated by SWGIT members. The migration to new imaging technology may significantly affect current work processes and should be done only after examining current operating procedures and completing a needs assessment. This should involve the participation of the organizations imaging and/or subject matter experts. Examining current operating procedures is the crucial first step in implementing new imaging technology. Consideration 1: Needs Assessment 1 Prior to selecting digital imaging technology, current practices must be examined to determine if there is a need to replace or enhance existing technology. Consideration should be given to a hybrid imaging system where some or all of the current equipment is used in conjunction with a new technology. Consideration 2: Cost Analysis 1 Prior to selecting a digital imaging system, a cost-benefit analysis must be conducted to determine the cost justification of a system purchase and to determine the possible advantages and disadvantages to the agency with its implementation. This analysis would allow a financial comparison between the current and proposed imaging systems to make a procurement decision. To determine a cost estimate, the following components should be considered: system hardware, software, and maintenance; application software; communications hardware and software; training; project management; facilities upgrades and site preparation; and staffing and miscellaneous costs. A typical cost justification includes the following major areas: a study of current operations, proposed system architecture, equipment pricing, and financial indicators, including a payback period. Consideration 3: Image Resolution 1 When determining resolution requirements, the intended usage, data storage requirements, and the need for accurate reproduction of the image must be considered. SWGIT Guidelines for the Forensic Imaging Practitioner 1
Consideration 4: Image Storage 2 Original images must be preserved on separable media. The selection of a storage media may depend on budget considerations for the agency. Each has its own advantages and disadvantages. Consideration 5: Image Compression 3 Compression affects image quality and should be considered carefully. Lossy compression, such as JPEG, can result in the loss of critical details. The use of this type of compression may render an image unsuitable for forensic analysis. Consideration 6: Equipment Evaluation Information used to evaluate suitability of new imaging technology should include feedback from agencies currently using the equipment in similar applications, product reviews, and vendor specification sheets. Prior to making a final selection, require a demonstration of new imaging technologies using representative samples of casework. Do not rely solely upon prepackaged demonstrations. Consideration 7: Standard Operating Procedures (SOPs) SOPs must be developed to ensure consistency, quality, integrity, and repeatability of the process. A staff member should be responsible for the overall project management, system administration, and maintenance of the SOPs. It is the responsibility of a staff member, rather than vendors and manufacturers, to maintain written documentation of system procedures and SOPs, including access and security policies and procedures. Consideration 8: Training 4 Initial and continuing training in imaging technology is required. 2 Consideration for Managers
Version 1.2 2001.12.06 Consideration 9: Recurring Costs Administrative managers should be aware of the cost of maintaining and upgrading imaging systems. Unless these costs are factored into the budget, the system is in danger of becoming obsolete. Some agencies annually budget approximately 15 percent of the original system acquisition cost for upgrades, training, and maintenance. Consideration 10: Legal Considerations SOPs should be designed to protect the integrity of the images. The user should be familiar with how the rules of evidence apply. 1 See SWGIT Guidelines for Field Applications of Imaging Technologies 2 See SWGIT Guidelines for the Use of Imaging Technologies in the Criminal Justice System 3 See SWGIT Recommendations and Guidelines for the Use of Digital Image Processing in the Criminal Justice System 4 See SWGIT Guidelines and Recommendations for Training in Imaging Technologies in the Criminal Justice System SWGIT Guidelines for the Forensic Imaging Practitioner 3
Version 2.3 2001.12.06 Section 3 Guidelines for the Field Applications of Imaging Technologies in the Criminal Justice System Introduction The purpose of this document is to: Provide specific recommendations and guidelines for the use of imaging technologies in law enforcement field applications. Describe the advantages and disadvantages of silver-based film cameras, instant photography cameras, digital still cameras, video cameras, and hybrid imaging systems in law enforcement field applications. Provide general guidelines for preparing agency-specific imaging technologies standard operating procedures (SOPs) for law enforcement field applications. Provide imaging equipment recommendations. This document addresses the photographic documentation of events or subjects that are not in a controlled environment (e.g., forensic laboratory or studio). The field applications addressed in this document include the following imaging: General crime scene photography First responder (FR) photography When crime scene photography personnel will not be called Prior to arrival of crime scene photography personnel Surveillance photography Tactical surveys Hazardous materials (HAZMAT) crime scene photography Aerial photography Accident scenes Arson photography Autopsy photography SWGIT Guidelines for the Forensic Imaging Practitioner 1
Bomb scene photography Mass disaster photography Search warrant photography Gang-related graffiti photography (FR) Field mug shots and tattoos (FR) Victim photography Advantages and Disadvantages of Major Image Capture Technologies in Field Applications The selection of an acquisition device (camera) is driven by the purpose and requirements of the end product. Therefore, the final use of the image should determine the choice of the camera. The recommendations for primary and secondary image capture devices are dependent on current technology and may change subject to changes in technology. These recommendations are made based on the practical experience of the SWGIT membership in the acquisition and analysis of the images discussed herein. Agencies should decide what technologies are best suited to meet the requirements of their mission-specific tasks. As long as an agency can demonstrate and document that its choice of technologies is adequate to meet its anticipated needs, the agency should not feel required to adhere to the SWGIT recommendations. Silver-Based Film Cameras It is strongly recommended that a camera capable of manual override, with interchangeable lenses, off-camera flash, and a tripod mount be used as the primary capture device along with conventional silver-based film in 35 mm format or larger as the primary capture media for evidentiary photography/imaging. Advantages of silver-based film cameras in field applications: Highest resolution of available image capture options Highest dynamic range of available image capture options Best color range of available image capture options Most flexibility of currently available image options Most durable storage medium More readily available in the field than video or digital storage media 2 Guidelines for the Field Applications of Imaging Technologies in the Criminal Justice System
Disadvantages of silver-based film cameras in field applications: Need for separate processing/printing facilities Relatively long processing time Environmental hazards generated by processing byproducts Version 2.3 2001.12.06 Preprocessing fragility (i.e., temperature, humidity, x-ray effects, expiration) No means of immediate image evaluation (with the exception of instant film) Discussion Resolution: The best measure of resolution is the evaluation of output imagery, which is the product of a series of steps. However, since this document is devoted to field applications, the following discussion is restricted to camera evaluation only. Users should verify resolution by visually examining images of test targets in their specific environments. SWGIT uses the following definitions of resolution: "Measure of capability to delineate picture detail;" and "The ability of a photographic system to record fine detail." These definitions are a subset of those found in ANSI/A Technical Report TR26-1993: Resolution as it Relates to Photographic and Electronic Imaging. Traditionally, film manufacturers measure resolution in terms of line pairs per millimeter (LP/mm) or lines per millimeter. Figure 1 illustrates how a line pair consists of a black line and an adjacent white line. Lines per millimeter refers to each line (black or white), thus there are always twice as many lines as there are line pairs over a given distance. Manufacturers of digital cameras frequently describe image size in terms of number of pixels. As stated in ANSI/A TR26-1993, "There is a common practice of referring to digital resolution as simply the total number of pixels within a frame or field, or alternately as the number of pixels in the horizontal and vertical directions. Alone, this information is useful to Figure 1 Conventional Film Resolution in Terms of Line Pairs per Millimeter (Lp/Mm) or Lines per Millimeter. indicate the amount of data that can be handled in a single field at a given moment, but tells nothing about the unit's ability to resolve spatial information." (Note that the words frame and field in the quote refer to a photographic field of view. These should not be confused with the terms used in video technology.) The ability to resolve spatial information can only be determined by testing a specific imaging system. In order to compare technologies, the total information that can be represented in the sensor is discussed. This constitutes an upper limit to the actual SWGIT Guidelines for the Forensic Imaging Practitioner 3
represented in the sensor is discussed. This constitutes an upper limit to the actual achievable resolution. It is possible to directly compare the maximum amount of information that can be represented by any two sensors by comparing the total number of pixels per frame. To compare film to the sensors in digital cameras (CCD/CMOS), it is necessary Figure 2 Relating Line Pairs per Frame to Pixels per Frame under theoretically ideal conditions. Each Line Pair corresponds to two-pixel columns. to relate line pairs per frame to pixels per frame. Figure 2 illustrates how, under ideal conditions, two pixel columns(or rows) represent one line pair. Common film types encountered in law enforcement field applications have optimal resolutions in the range of 40-160 line pairs per millimeter. Black and white films typically used at crime scenes have resolutions at the upper end of this range. Color films used at crime scenes have resolutions at the lower end of this range. A single frame of 35 mm ISO 200 color film is 36 mm wide by 24 mm high. With a resolution of 50 line pairs per millimeter, such a frame can resolve the following: 36mm x 50 LP/mm = 1800 line pairs horizontally and 24mm x 50 LP/mm = 1200 line pairs vertically. The equivalent number of pixels in a single frame is then calculated: 1800 line pairs x 2 pixels/line pair = 3600 pixels horizontally and 1200 line pairs x 2 pixels/line pair = 2400 pixels vertically. This represents a total of 3600 x 2400 = 8,640,000 pixels. A digital camera with a detector that is 3040 x 2008 pixels in size contains more than six million (6,104,320) pixels. This is referred to as a 6-megapixel camera. There is a tradeoff between the field of view and the resolution that can be represented by a sensor. If the field of view is held constant, then the resolution will vary with the number of pixels. If resolution is held constant, then the field of view will vary with the number of pixels. 4 Guidelines for the Field Applications of Imaging Technologies in the Criminal Justice System
If the field of view is held identical for both sensors above (35 mm ISO 200 color film and a 6- megapixel CCD), the film, with 40 percent more pixels than the CCD (8.64 million versus 6.1 million), will provide an improvement in resolution of approximately 20 percent. Version 2.3 2001.12.06 Alternatively, if the resolution is held constant for both sensors, the film will cover a field of view that is 40 percent larger than the CCD, as illustrated by Figure 3. The resolution that can be achieved in a digital camera will be lower than the upper limit (ideal conditions) discussed above. Some research has found that it takes approximately four pixels to capture and reproduce a line pair under test conditions, instead of the representation by two pixels. Using this standard, the pixel resolution of film is effectively doubled. The practical result of using four pixels per line pair leads to the comparisons in Table 1 and Figure 4. Figure 3 Comparison of Field of View 35 mm ISO 200 Color Film versus 6-Megapixel CCD for Constant Resolution. NOTE: Discussing the Figure 4 Relative Field of View for different sensors at resolution of video systems comparable resolution. is beyond the scope of this document. SWGIT will address issues relating to video resolution in future documents. To compare the size of images generated from each of these sensors, a common output resolution must be defined. A conservative divisor of 200 pixels per inch (ppi) is generally used to determine the output size. Table 2 lists the size of the images generated using the sensor resolutions in Table 1. In the above discussion, only film and digital sensors were considered. In reality, an image is captured and later displayed using an entire system in which several factors may affect the resolution of the particular image. The quality of the optics (lens or lenses) used to focus the image on the sensor plays an extremely important role and may greatly limit the overall resolution of the system. Also, differences in display SWGIT Guidelines for the Forensic Imaging Practitioner 5
may greatly limit the overall resolution of the system. Also, differences in display methods may limit or enhance the perceived resolution. CCD sensors often achieve color acquisition by using one sensor array with pixel cells of alternating color sensitivity. Thus the overall resolution of the image will be less than the specified number of pixels on the sensor. One way to ameliorate this situation is to use a camera that contains three CCDs instead of one. This allows one to have a separate CCD for each primary color, red, green, and blue. Therefore, for the same specified number of pixels at the sensor, a three-ccd camera will provide higher resolution than a single-ccd camera. Two other factors that can affect resolution include the contrast in the scene and noise. In this context, contrast refers to the apparent difference between the brightest and darkest parts of the scene. As contrast increases, resolution increases. Noise refers to random variations that limit the fidelity of detection and reproduction systems, such as the granularity of photographic images. As noise increases, resolution decreases. Identifying the specific effects of these factors on each of the sensors discussed above is beyond the scope of this document. Dynamic Range: The difference between the brightest highlight and darkest value that a sensor (film or CCD) can detect and record in a single image. Negative film provides two to four f-stops more than most digital cameras. This increased dynamic range allows capture of both shadow and highlight details in a single frame of film. These same details might require several different images (at different capture settings) when recorded with a digital camera. Color Range: The range of colors that can be detected by a sensor compared to normal human vision. Negative film has a color range that is superior to CCDs. Flexibility: The selection of speeds and types of film available. Silver-based photography provides a wider selection of film speeds and types than digital cameras. Film can be selected for specific applications in the field, and the film speed or type can be changed on-site to meet specific needs. Instant Print Cameras Advantages of instant print cameras in field applications: Immediacy of the final image (instant viewing/verification of image) Operational security (all processing is in-house) Disadvantages of instant print cameras in field applications: Limited resolution of image Production of copies requires multiple steps and can reduce image quality High cost per image Manual override, interchangeable lenses, or off-axis flash rarely offered 6 Guidelines for the Field Applications of Imaging Technologies in the Criminal Justice System
Version 2.3 2001.12.06 Digital Cameras Advantages of digital cameras in field applications: Immediacy of the final image (instant viewing/verification of image) Ability to transmit and disseminate image with minimum of intermediate steps On-site image management Potential for on-site printing Operational security (all processing is in-house) Environmental impact more friendly than film Disadvantages of digital cameras in field applications: Battery or power supplies: Environmental impact Availability Power conversion Limited availability of storage media (available only from specialized stores) Storage media subject to damage from electromagnetic fields Image acquisition subject to electromagnetic interference Hardware and software can be proprietary and incompatible among manufacturers Legacy file problem (evolution of technology, including hardware and software, may impact ability to access archived images over time) Video Cameras NOTE: Fixed camera video surveillance systems are not addressed in this document. They will be addressed in future SWGIT documents. Advantages of video cameras in field applications: Real-time motion record capability Immediacy of image (instant viewing/verification of image) Ability to transmit and disseminate image with minimum of intermediate steps SWGIT Guidelines for the Forensic Imaging Practitioner 7
More environmentally friendly than film Ability to print in the field Ability to synchronize and capture audio Disadvantages of video cameras in field applications: Battery or power supplies: Environmental impact Availability Power conversion Some high-quality storage media available only from specialized stores Storage media subject to damage from electromagnetic fields Image acquisition highly subject to electromagnetic interference Resolution of still images is less than that of digital or silver-based capture media Limited color fidelity (VHS and 8 mm formats, in particular) Reduced media lifetime Automatic compression in some formats Weight and portability of equipment may be an issue Notes on video formats: VHS and 8 mm formats are the most commonly available formats but have the worst signal-to-noise ratio of any video format (greatest amount of noise). Super VHS and Hi-8 formats are the second most commonly available formats and have somewhat better signal-to-noise ratio than VHS. Beta SP and MII formats are professional-broadcast quality and are the best analog format available. Digital video quality varies, the high end is better than analog systems. Hybrid Imaging Systems A hybrid system is the combination of silver-based photography and digital imaging technology that typically involves the conversion of silver-based film or print images to digital images through the use of scanners. Hybrid imaging systems incorporate some of the benefits of both film and digital image technologies and are recommended for those agencies and organizations seeking to add digital imaging technologies to their photographic resources. 8 Guidelines for the Field Applications of Imaging Technologies in the Criminal Justice System
Version 2.3 2001.12.06 photographic resources. Advantages of hybrid imaging systems in field applications: Shortens darkroom time for producing prints Maintains high-quality original film images Offers flexibility of digital image processing Enables easy electronic transmission of images Enables image analysis Simplifies case file management Enables the use of a variety of output devices Permits the production of copies from prints generated through instant photography Disadvantages of hybrid imaging systems in field applications: Separates processing/printing facilities Has a relatively long processing time Generates environmentally hazardous byproducts Demonstrates a preprocessing fragility (i.e., temperature, humidity, x-ray effects, expiration) Has no means of immediate image evaluation (with the exception of instant film) Guidelines for Standard Operating Procedures (SOPs) General Guidelines for a Crime Scene Photography SOP TITLE: Crime Scene Photography SOP PURPOSE: To permanently document, by qualified personnel, evidence and other details at a crime scene for future reference NOTE: Crime scene photography generally requires the ability to: Record information that crime scene personnel may not know was important at the time the images were captured Deal with varying lighting and physical conditions SWGIT Guidelines for the Forensic Imaging Practitioner 9
Accurately represent the details and colors in a scene Get close-up and wide-angle images with accurate spatial relationships Crime scene photography is usually a time-limited activity when there is only one opportunity to correctly complete the task. Depending on the nature of the crime or incident, conditions at a crime scene may dictate the selection and use of differing equipment and techniques. EQUIPMENT: (Image Capture Devices) Silver-based film cameras are recommended for use as the primary image capture device. The minimum recommendation is a 35 mm (SLR) camera capable of manual override, interchangeable lenses, off-camera flash, and tripod mount Digital still imaging can be used in a supplementary capacity (see Digital Cameras). Digital still imaging can be used as the primary image capture device when the performance of the equipment can be shown to meet anticipated needs Video imaging can be used in a supplementary capacity. S-VHS, Hi-8, or betterquality formats are recommended. It is suggested that cameras have the ability to incorporate external/wireless audio, the ability to disable on-camera audio, and incorporate/disable in-camera image stabilization (See Video Cameras) Other standard photographic equipment as necessary PROCEDURES: Agencies should follow agency-specific step-by-step instructions for documenting crime scene evidence. CALIBRATION: If necessary, agencies should develop procedures specific to their needs. CALCULATIONS: If necessary, agencies should develop procedures specific to their needs. LIMITATIONS: See Advantages and Disadvantages of Major Image Capture Technologies in Field Applications SAFETY: Agencies should develop procedures specific to their needs. REFERENCES: Agencies should refer to agency-specific documentation and manufacturers' manuals. General Guidelines for a First Responder (A) SOP The only images taken are those taken by the first responding officer(s). TITLE: First Responder Photography SOP PURPOSE: To document conditions found at an incident by the first law enforcement official(s) on the scene where a crime scene photography unit or specialist will not be 10 Guidelines for the Field Applications of Imaging Technologies in the Criminal Justice System
Version 2.3 2001.12.06 official(s) on the scene where a crime scene photography unit or specialist will not be requested. NOTE: Examples may include: domestic violence incidents, traffic accidents, minor property crimes, and other incidents as defined by agency-specific policies. Photography generally is not the first responder's primary responsibility, and the first responder may have only a minimal amount of photography training. EQUIPMENT: (Image Capture Devices) Silver-based media film camera. Minimum recommendation is a 35 mm camera with flash and close-up capability Digital still imaging. The minimum recommendation is for a camera with more than 1600 x 1200 pixels (>2 megapixels), on-camera viewer, close-up capability, flash, and removable storage media Video imaging can be used in a supplementary capacity. S-VHS, Hi-8, or betterquality formats are recommended. It is suggested that cameras have the ability to incorporate external/wireless audio, disable on-camera audio, and incorporate/disable in-camera image stabilization (See Video Cameras) Other standard photographic equipment as necessary PROCEDURES: Agencies should follow agency-specific step-by-step instructions for documenting crime scenes. NOTE: Images from separate incidents should be clearly delineated through a change of storage media or through proper documentation. CALIBRATION: If necessary, agencies should develop procedures specific to their needs. CALCULATIONS: If necessary, agencies should develop procedures specific to their needs. LIMITATIONS: Successful capture of close-up images will require adhering to manufacturers' specifications. Images captured digitally typically have a limited enlargement capability that is less than those captured using 35 mm film (See Advantages and Disadvantages of Major Image Capture Technologies in Field Applications). Successful capture of images also requires utilization of fresh media (e.g., film that is not past expiration and has been stored properly) and wellmaintained equipment. SAFETY: Agencies should develop procedures specific to their needs. REFERENCES: Agencies should refer to agency-specific documentation and manufacturers' manuals. SWGIT Guidelines for the Forensic Imaging Practitioner 11
General Guidelines for a First Responder (B) SOP Images taken by the first responding officer(s) prior to arrival of a crime scene photographer. TITLE: First Responder Photography SOP PURPOSE: To document conditions found at an incident by the first law enforcement official(s) on the scene prior to the arrival of a crime scene photographer NOTE: This guideline is directed toward documenting transient conditions that might be lost prior to the arrival of crime scene photographers. Examples include situations in which evidence must or might be moved, lost, or altered. Photography generally is not the first responder's primary responsibility, and the first responder may have only a minimal amount of photography training. EQUIPMENT: (Image Capture Devices) Silver-based media film camera. The minimum recommendation is 35 mm camera with flash, close-up capability Digital still imaging. The minimum recommendation is for a camera with more than 1600x1200 pixels (>2 megapixels), on-camera viewer, close-up capability, flash, and removable storage media Video imaging can be used in a supplementary capacity. S-VHS, Hi-8, or betterquality formats are recommended. It is suggested that cameras have the ability to incorporate external/wireless audio, disable on-camera audio, and incorporate/disable in-camera image stabilization (See Video Cameras) Other standard photographic equipment as necessary PROCEDURES: Agencies should follow agency-specific step-by-step instructions for documenting crime scenes. NOTE: Images from separate incidents should be clearly delineated through a change of storage media or proper documentation. CALIBRATION: If necessary, agencies should develop procedures specific to their needs. CALCULATIONS: If necessary, agencies should develop procedures specific to their needs. LIMITATIONS: The successful capture of close-up images will require adhering to manufacturers' specifications. Images captured digitally or with video typically have a limited enlargement capability that is less than those captured using 35 mm film (See Advantages and Disadvantages of Major Image Capture Technologies in Field Applications). Successful capture of images also requires using fresh media (e.g., film that is not past expiration and has been stored properly or new, unused videotapes) and well-maintained equipment. 12 Guidelines for the Field Applications of Imaging Technologies in the Criminal Justice System
Version 2.3 2001.12.06 and well-maintained equipment. SAFETY: Agencies should develop procedures specific to their needs. REFERENCES: Agencies should refer to agency-specific documentation and manufacturers' manuals. General Guidelines for a Surveillance Photography SOP TITLE: Surveillance Photography SOP PURPOSE: To document acts and individuals engaged in those acts as they occur. NOTE: Surveillance activities may involve highly specialized techniques and equipment that require technical training and knowledge and are best accomplished by trained specialists. EQUIPMENT: (Image Capture Devices) Silver-based media film camera. The minimum recommendation is a 35 mm camera with capability to disable both the flash and infrared auto-focus transmitter Digital still imaging. The minimum recommendation is for a camera with a minimum pixel resolution of 2000 x 1500 pixels (3 megapixels), capability to accommodate long telephoto lenses, and disable the flash and infrared autofocus transmitter. In covert surveillance situations, illumination of the photographer by the LCD screen may compromise safety Video imaging can be used in a supplementary capacity. S-VHS, Hi-8, or betterquality formats are recommended. It is suggested that cameras have the ability to incorporate external/wireless audio, disable on-camera audio, and incorporate/disable in-camera image stabilization (See Video Cameras) Other standard photographic equipment as necessary NOTE: State laws may limit the legality of audio taping. Check local statutes for legality of all surveillance activities. SPECIALIZED EQUIPMENT: Night vision or thermal imaging equipment PROCEDURES: Agencies should follow agency-specific step-by-step instructions for documenting crime scenes. If audio is used, simultaneous recording of audio with video on the same media and testing of the system is strongly recommended. CALIBRATION: If necessary, agencies should develop procedures specific to their needs. CALCULATIONS: If necessary, agencies should develop procedures specific to their needs. SWGIT Guidelines for the Forensic Imaging Practitioner 13
LIMITATIONS: The successful capture of images sufficient for identification of depicted individuals and/or objects (e.g., license plates) will require close attention to the selection and appropriate use of equipment. Images captured digitally or with video typically have a limited enlargement capability that is less than those captured using 35 mm film (See Advantages and Disadvantages of Major Image Capture Technologies in Field Applications). The successful capture of images also requires utilization of fresh media (e.g., film that is not past expiration and has been stored properly or new, unused videotapes) and well-maintained equipment. SAFETY: Agencies should develop procedures specific to their needs. REFERENCES: Agencies should refer to agency-specific documentation and manufacturers' manuals. General Guidelines for a Tactical Survey SOP TITLE: Tactical Survey SOP PURPOSE: To document conditions at a location so that plans can be made for future law enforcement activities NOTE: This type of photography is directed at obtaining general information regarding the physical layout and major contents of a location in preparation for law enforcement activities. EQUIPMENT: (Image Capture Devices) Silver-based media film camera. Minimum recommendation is 35 mm camera Digital still imaging. Minimum recommendation is for a camera with more than 1600 x 1200 pixels (>2 megapixels) Video imaging can be used in a supplementary capacity. S-VHS, Hi-8, or betterquality formats are recommended. It is suggested that cameras have the ability to incorporate external/wireless audio, disable on-camera audio, and incorporate/disable in-camera image stabilization (See Video Cameras) Other standard photographic equipment as necessary PROCEDURES: Agencies should follow agency-specific step-by-step instructions for documenting crime scene locations. CALIBRATION: If necessary, agencies should develop procedures specific to their needs. CALCULATIONS: If necessary, agencies should develop procedures specific to their needs. LIMITATIONS: Location-specific limitations may apply. 14 Guidelines for the Field Applications of Imaging Technologies in the Criminal Justice System