July 8, 2004
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
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.
Richard W. Vorder Bruegge
Follow this link to view the Digital
Imaging Procedure document.