DVRs That Deliver

The working group tasked with drawing up the UK police requirements code relating to the use of cctv footage as evidence in a court of law has consulted widely with bodies including the Association of British Insurers, Law Society and Home Office Scientific Development Branch.

Input has also been gained from officers on the front line such as police forensic experts to help shape and strengthen the draft document.

This is a fast moving technology sector and the group was firm in its decision not to focus on the digital technology itself, but instead concentrate on what DVRs should deliver in terms of providing credible images to use as evidence in court.

Particular emphasis has been placed on areas including image quality and authenticity, storage and playback of these images, as well as audit trail procedures.

Looking at some of these in more detail, the code recognises that there are two key elements involved in ensuring image authenticity from DVRs, namely the areas of image protection / authentication techniques and the integrity of the DVR unit itself. In the past, the police gained reassurance when handling VHS tapes from being able to physically touch the original recording medium.

The difference when using digital technology is that evidence is extracted from the equipment’s hard drive and then copied onto removable media such as a CD/DVD, raising a number of question marks that the working group has sought to answer.

Image authentication techniques such as data encryption, a process called check summing (involving use of an algorithm base on unique key data) and digital watermarking are also reviewed in the code. Sufficient and demonstrable controls are required to prevent unauthorised access to storage media, while playback of electronic images should conform to a number of parameters including the key area of time and date information integrity.

One way in which DVRs offer advantages over older tape recording and storage technology lies in their ability to digitally enhance images in a variety of different ways, an area the working group has tackled in the code by providing clear guidance relating to original or master images and the export of images for playback on different media.

Watertight evidence

The code additionally addresses the need for robust audit trail procedures to cover the processes that lead from the initial recording of the original images by CCTV camera right through to their subsequent presentation as evidence in court, so as to convincingly demonstrate they have not been tampered with at any point in between.

These procedures overlap with the need for correct operator training that covers the proper way to securely process evidential material.

One serious concern is that, unless these audit trails and operator procedures stand up to scrutiny in court, the Crown Prosecution Service may not be able to use the CCTV images in the first place or defence lawyers will later be able to pull holes in the evidence presented, potentially jeopardising the case and undermining a significant raison d’