SWGIT Photo Guidelines, Part 2 (FSC, October 1999)
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October 1999 - Volume 1 - Number 3 |
Definitions and Guidelines for the Use of Imaging Technologies in the Criminal Justice System
Part II: Guidelines
(Version 2.1 — June 8, 1999)
Documentation of Policies and 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.
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 formats. 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, and reliability:
- Silver-based film with the exception of instant film
- Write-Once Compact Disk Recordable (CDR)
- 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:
- Instant film separately fixed
- Photographic prints
- 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:
- Instant film packs
- Inkjet prints
- Solid ink prints
- Thermal wax paper prints
- 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 the 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 the 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.
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 steps should be documented in the case notes in sufficient detail that comparably trained personnel can repeat the steps and produce similar output.
Preserving Original: Chain of Custody
A chain of custody must be maintained for the film or video tape upon which original images are recorded.
For digital images, the chain of custody should document the identity of the personnel who had custody and control of the digital image file from the point of capture to archiving. Once the file has been archived, the chain of custody should document the identity of the personnel who had custody and control of the archived image.
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.
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 because critical image information could be lost and artifacts introduced as a result of the compression process. Repeated saving of a file using lossy compression may exacerbate the loss of image information.
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 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)
It is strongly recommended that conventional silver-based film be the primary media for documenting crime scenes. This documentation may be supplemented by analog video and/or digital imaging.
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
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
Return to beginning of document
Part III: Standard Operating Procedures
Part V: Training, Qualifications, and Proficiency
Information referenced to this document can be identified as Version 2.1 ¾ June 8, 1999.