Crack this code

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 a court of law.

Now the British Security Industry Association is publishing a new Code of Practice to assist in the specification, selection, installation and operation of DVR equipment.

The code is a major development in the acceptance of digital video, says BSIA CCTV Section Chairman, Adam Wiseberg.

"Ensuring that digital CCTV footage is admissible in court is dependent on a number of factors including: image quality and authenticity; storage; the method used to export images; playback; operator/owner awareness; and a comprehensive audit trail.

The code provides authoritative guidance on all these areas and should supply installers, the police, end-users and insurers with the information they need to use digital technology to its maximum potential. Says Wiseberg: "Ultimately, we want to make sure that there is an independent benchmark in place so there can be the same confidence in the validity of digital media in the criminal justice system as there is in VHS tape from a traditional VCR."

It has been produced following wide consultation with interest groups including the Home Office Scientific Development Branch.

In launching it, the BSIA CCTV Section acknowledged the pioneering work of the late Mike Constant, security consultant, in calling for the development of a standard in this area.

So what does the new code say?

Here is Security Installer's summary of the code. While this highlights important points, it is essential that installers see the full code which can be downloaded from the BSIA website: www.bsia.co.uk

While the code points out the the many advantages of DVR technology, it does not attempt to establish a preference for the digital recording medium to be adopted. It does, however, recommend the areas that should be considered.

Particular emphasis is placed on the key areas: Image quality; Admissibility as evidence; Image authenticity; Storage; Export of images; Playback; Operator/owner awareness; and Audit trail.

Existing reference documents are indispensable for the application of the code and these are listed, along with terms and definitions, in the document.

Image quality

Before evaluating image quality, ensure that the reason for recording the images is clearly defined and understood. Choose the highest image quality of system as possible, ensuring that the images produced are fit for that purpose.Always take the following factors that affect image quality into account subject size within the field of view of the camera lighting of subjects within field of view

• camera & lens specification
• recorded digital image compression
• image per second record rate per camera
• transmission medium
• system maintenance
• recorded digital image resolution
• Admissibility as evidence

The House of Lords Select Committee on Science and Technology Session 1997-8 said that digital recording technology provides no original that could be produced in evidence. All that is available for use as evidence is a copy of the first, probably temporary, recording in memory, and this will be admissible.

• Its weight and admissibility will depend on:
• whether or not the image's audit trail from the recorder to the court is robust
• whether or not the integrity of the image can be proven.
• It is at the court's discretion whether or not the evidence is deemed admissible.

Audit trail

It is important that actions and events for the recording system are logged.

This should cover the period from when the original recorded images are recorded to media up to the point which, the police or prosecuting authority take control of the master or evidential copy or it is no longer required.

Image authenticity

It is important that the integrity of the images from the DVR can be proven, in a way that the original recorded images and subsequent copies cannot be altered without detection.

Various techniques can be employed to detect image tamper - for example digital fingerprinting, digital watermarking and checksumming (when an image is checksummed according to an algorithm based on unique key data).

The DVR manufacturer should be capable of providing a statement that can be used in defence of the authentication method.

Storage

Data encryption: This scrambles the digital data that forms an image in such a way that it would be difficult to reconstruct into the original recorded image - but remember, data encryption should not prevent authorised users / organisations from gaining access to playback of the exported images.

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 be logged via an access control system or via an audit trail.

Recording retention: Careful consideration should be given to how long images are required to be stored. Allowance should be made for event discovery through to playback/export by all interested parties. The quality of images should not be compromised to increase storage period.

Storage functionality: The system must be intuitive and assist the user in management of the system. Users need to see how much recording they are receiving on their particular site. The DVR system should indicate how many days and hours of recording it has stored and it should indicate an estimated retention period based on the changing of settings.

Removable storage media: Where this is used as primary storage, care is required in how that physical 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. But it should be noted that:

a) 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;

b) if the media is removed or returned without appropriate auditing, then it constitutes an uncontrolled copy, which could reduce its evidential value.

Export of images

Image enhancements: DVRs may provide enhancement tools such as image sharpening, brightening or zooming in on a particular part of the image. Any applied enhancements must not change the 'original recording' or 'master copy' images. If an enhanced image is exported, an audit trail must exist.

The following should be adhered to:

• A trained operator and simple user guide should be available locally;
• The operator should know the retention period of the system and approximate times to export small (15 mins), medium (e.g. 24 hrs), large several days (up to all of the system) amounts of data;
• the software needed to replay the images should be included at export so viewing by authorised third parties is not hindered;
• export of a DVR event log, audit trail and any system settings with the images will assist with establishing the integrity of the images/system;
• the amount of video that will need to be exported will be dependent on the nature of the investigation. It is essential that the system is capable of doing this quickly and to an appropriate medium;
• export and recording should be possible at the same time without affecting performance;
• the system should not apply any compression or format conversion to the image when it is exported, as this can reduce the usefulness of the content;
• export of the original signature i.e. digital fingerprinting, checksumming, digital watermarking should be carried out to ensure image authenticity;
• hardware used for exporting images should be capable of verifying export was successful.

Export media

This should be proportionate to the amount of data. A number of scenarios exist on how to export images from a DVR:

• the image is printed onto paper
• the image is copied (locally or remotely) to some form of removable digital media such as a floppy disk, DAT tape, flash card, CD-RW, hard disk, DVD
• the removable hard disk is physically removed from the DVR; the images are played back on the DVR to enable them to be recorded onto a conventional analogue VCR tape.

Export file format: 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.

Exporting supporting data: The time and date information with any associated metadata should be exported with the images. If the DVR supports event logging and audit trails then the facility for saving the DVR's settings and its event log/audit trail should be provided.

Playback of exported images

Where the export media is intended to be replayed on a PC, the playback software should:

• have variable speed control including frame-by-frame forward and reverse viewing.
• display single and multiple cameras and maintain aspect ratio i.e. the same relative height and width.
• display a single camera at the maximum record resolution.
• permit the recordings from each camera to be searched by time and date.
• allow printing and/or saving (e.g. bitmap) of pictures with time and date.
• allow for time synchronised multi-screen playback.
• allow for time synchronised switching between cameras upon playback.
• allow playback of associated audio and other metadata.
• The time and date, and any other information associated with each picture should be legible and should not obscure the image.

Time and date integrity

General: The time and date information of the system is key. The user should ensure that the time and date (including time zones) is correct and that it is checked regularly.

Synchronisation: Multiple DVRs should provide a method of time and date synchronisation, either manually or automatically. Daylight saving time changes should also be accommodated.

• The title of the BSIA document is Code of Practice for Digital Recording Systems for the Purpose of Image Export to be used as Evidence
• There are an estimated 4.25 million CCTV cameras in the UK - more cameras per head than any other country in the world.
• The BSIA CCTV Section has 73 member companies employing 4000 staff and the association estimates that its members have a 90 per cent market share.