October 2004 - Volume 6 - Number 4

Standards and Guidelines

Digital Imaging Procedure

Police Scientific Development Branch
United Kingdom

July 8, 2004

Dear Colleagues,

A number of law enforcement officials in North America approached the Scientific Working Group on Imaging Technology (SWGIT) requesting guidance in developing policies and procedures to acquire and protect their digital image evidence. Many expressed concern regarding potential challenges to the integrity of digital images.

SWGIT is pleased to present Digital Imaging Procedure, Version 1.0. This document was published by the United Kingdom’s Police Scientific Development Branch, which has agreed to let us distribute it. This document addresses the issues of digital image acquisition and integrity in a straightforward manner that is consistent with the guidelines and recommendations of SWGIT.

SWGIT strongly encourages agencies to incorporate the recommendations provided in this document in their own policies and procedures, as appropriate. In doing so, agencies will be taking an important step to ensure the integrity of their digital image evidence.

Among the most critical fundamental ideas presented in this document is the concept of a master copy, which serves as the digital equivalent of an original film negative or video tape. A master copy represents either a bit-for-bit duplicate of original digital files or a digital copy of an analog recording that has been written to removable media, such as a compact disc or DVD-R. When a master copy is generated, it can be handled using the same policies and procedures an agency would use to protect and preserve the integrity of an original film negative or video tape.

As Digital Imaging Procedure, Version 1.0 points out, although it is commonly accepted that a credible manipulation of digital image files can be accomplished relatively easily, it is very difficult to conceal manipulation when the manipulated file is compared to the master file. Thus, creating a master copy represents the most critical step in any procedure involving digital image files.

Another important concept discussed in this document is that imaging devices (i.e., film, video, or digital still cameras) do not duplicate or clone reality but merely generate a visual representation of a subject. The degree to which an image represents a lifelike simulation of reality will be a function of many factors, including the type of camera used, the processing applied to the image, and the means by which the image is displayed. Agencies and personnel using images should be aware of the capabilities and limitations of different technologies. Furthermore, agencies must develop policies and procedures that enable them to generate images of sufficient quality to accomplish their mission.

Some of the guidance in this document may only apply to agencies in the United Kingdom. Agencies implementing the guidelines elsewhere should ensure that they meet statutory requirements in their jurisdiction.

SWGIT will continue developing guidelines for the use of imaging technology in the criminal justice system. We will also continue to work with our international partners to identify similar documents and guidelines that will be of benefit to our local community. We hope you find this document of assistance in your work.

Sincerely,
Richard W. Vorder Bruegge
SWGIT Chair