The prolific uptake of digital video recording by the CCTV industry has led to a pressing need for definitive guidance where digital video images are being used as evidence in the criminal justice system. Thankfully, this is an area which the British Security Industry Association (BSIA) has sought to address with the development of a bespoke Code of Practice.
Publication of the Code – entitled the ‘Code of Practice for Digital Recording Systems for the Purpose of Image Export to be Used as Evidence’ – follows a period of extensive consultation with a number of interested parties (including the Association of British Insurers, the Law Society and the Home Office Scientific Development Branch) as well as input from police forensic experts, all of whom have helped in shaping and strengthening the text.
A combination of insufficient cleaning and maintenance, the overuse of VCR tapes, inadequate lighting and lax operational procedures has often led to problems in identifying potential crime culprits from CCTV images. Sadly, this issue was perfectly – but also brutally – brought into focus 13 years ago, when the original pictures showing toddler Jamie Bulger and his abductors at a Merseyside Shopping Centre had to be enhanced by a Police Technical Support Unit before they could be used as part of the ensuing investigation.
Improvements introduced since then – at least in part as a result of publicity surrounding the Bulger case – have brought the question of quality recordings into the spotlight. Installers and system users alike have begun to recognise their true importance, in particular from the mid-1990s as digital video recorders (DVRs) have been specified for commercial use in ever-increasing numbers.
High profile test for recordings
A major public test of how well digital technology can cope came in the aftermath of last summer’s high profile 7/7 London terrorist explosions. The massive intelligence gathering exercise orchestrated by the Metropolitan Police Service and surrounding forces was significantly aided by the presence of surveillance systems covering the streets, London Underground stations and buses targeted in the attacks, as well as transport links elsewhere in the Capital and its environs.
The pictures subsequently produced – such as those taken at Luton Station of the 7/7 bombers on the way to their suicide missions – showed clear, identifiable renditions of the perpetrators, underlining the value of this monitoring method not just to the security forces but also members of the public.
With analogue VCR tape increasingly being superseded by digital recording, then, an urgent need has arisen for definitive guidance where digital video images are used as evidence within the criminal justice system. Over the past three decades, end users, the judicial system and the police have all become accustomed to dealing with tape-based evidence. Naturally, there will be a tendency to want to handle digital material in exactly the same manner as its analogue equivalent. The reality is that digital video evidence is different – a difference which, if dealt with correctly, can deliver hugely positive benefits.
By their very nature digital images do not degrade, it being perfectly possible to make copies without eroding detail or quality. For the criminal justice system and the police, this obviously requires a change of approach. With a standard VCR tape, detectives had the reassurance of being able to physically touch the original as this was the medium on which recordings were stored. Not so with digital, as images must be extracted from the hard drive, where the original evidence is stored, and copied onto removable media.
Until now, there have not been any Best Practice methodologies written for storing and retrieving images on digital equipment. At the BSIA, we believe that this Code of Practice is a major development in the overall weight given to digital video evidence within a Court of Law.
Ensuring that digital CCTV footage stands up in Court is dependent on a number of factors. These include image quality and authenticity, storage, the method used to export images, playback, operator/owner awareness and the overriding need for a comprehensive audit trail.
Let’s take a look at each of these areas in turn. Although we’ll highlight the most important points, it’s vital that end users access a copy of the full Code (which can be downloaded at www.bsia.co.uk/ download.html).
Also, bear in mind that, while the Code highlights the many advantages of DVR technology, it does not attempt to establish any preference for the digital recording medium to be adopted. Existing reference documents are vital for the correct application of the Code (as such these are listed, along with essential terms and definitions, in the full document).
Here, the focus is very much on the integrity of the reference image and the robustness of the audit trail from the recording device to Court – factors which will naturally influence the weight that evidence may be afforded by the Judiciary.
Before evaluating image quality, ensure that the reason for recording images is clearly defined. Choose the highest image quality of system as possible, ensuring all the while that the images produced are ‘fit for purpose’.
Always take the following factors that affect image quality into account: subject size within the field of view of a camera, lighting of subjects within the field of view, camera and lens specification, recorded digital image compression, image per second rate per camera, the transmission medium and recorded digital image resolution.
Open to the Court’s discretion
The House of Lords Select Committee on Science and Technology Session 1997-98 5th Report stated that digital recording technology provides no original image that could be produced in evidence. All that is available for evidential purposes is a copy of the first – and probably temporary – recording in memory. This will be admissible as evidence. It is at the Court’s discretion whether or not the evidence submitted is deemed admissible.
Following on from this, the Code of Practice considers the importance of the integrity of the DVR itself in preventing reference images stored on a digital recording product from being tampered with in any way.
Also included is a review of the techniques which can ensure integrity, specifically digital watermarking, data encryption, digital finger printing, checksumming (when a given image is checksummed according to an algorithm based on unique, key data) and time/date integrity. Visible watermarking describes visibly insignificant changes made to the pixel values to incorporate information which changes if the image file is altered.
Note that your chosen DVR manufacturer should be capable of providing you with a bona fide statement that can be used in defence of the authentication method employed.
Storing your information
Data encryption scrambles the digital data that forms an image in such a way that it would be difficult to build it back into the original recorded image form. A reverse algorithm would be needed to re-build the image. That said, always remember that data encryption should not prevent authorised users from accessing the playback of exported images.
In terms of security, it should be demonstrable that access to storage media by either physical or electronic means is sufficiently controlled to prevent unauthorised access. Approved access should always be logged such that there is a record of who did what and when (either via an access control system or a simple audit trail).
Before specifying your DVR system, careful consideration should be given to how long images need to be stored. Appropriate allowances should be made for event discovery through to playback/export by all interested parties. Whatever the scenario, the quality of images should never be compromised in order to increase the storage period. Many DVRs overwrite the oldest images when the storage capacity is reached regardless of the intended retention period, although most also include an image protection mechanism which allows the end user to manually or automatically protect images from being overwritten.
Where removable media is employed as the primary method of storage, much care must be shown in relation to how that media is used. While the removable media exists within the DVR under controlled access, the digital images on that media may be considered as both the original recording and master copy.
Should the media be removed for evidential purposes as part of a correctly-audited process, then that specific media could be considered as the master copy. If the media is removed (or returned) without appropriate auditing then it constitutes an uncontrolled copy, which could reduce its evidential value.
DVRs may provide enhancement tools such as image sharpening, brightening or zooming-in on a particular part of the image. Any applied enhancement must not change the ‘original recording’ or ‘master copy’ images. If an enhanced image is exported, then an audit trail must also exist.
To facilitate replay and export, a trained operator and simple User Guide should be available locally. That operator should know the retention period of the system and approximate times taken to export small, medium and large amounts of data. The software needed to replay images should be included at export, otherwise viewing by authorised third parties may be hindered.
Images from DVRs may be printed onto paper, copied to some form of removable media (floppy disk, DAT tape, flash card, CD-RW, hard disk or DVD) or the removable hard disk will be extracted from the DVR and the images played back such that they may be recorded on a conventional VCR tape. Wherever possible, the video and audio material should be exported in the DVR’s native file format, and should be an exact copy of the original recording/master copy.
Punching holes in submitted evidence
One serious concern is that, unless audit trails and operator procedures stand up to rigorous scrutiny in Court, the Crown Prosecution Service may not be able to use the images in the first place. Alternatively, defence lawyers will punch holes in the evidence presented, potentially jeopardising the case and undermining a significant raison d’etre of the system (not to mention wasting police time in piecing together that evidence).
