CCTV and imaging technology

This depends on the system, but the primary aim is to retrieve the video in its native format whenever possible. Listed below are the typical options for exporting video data.

1. Burning onto DVD or CD
2. Transfer to memory card such as Compact Flash®
3. Via a USB port onto external hard drive
4. Via a network connection
5. Through the removal of the system’s hard disk drive/s
6. By removing the actual digital CCTV recorder

Check our publication no. 21/06 - Retrieval of Video Evidence and Production of Working Copies from Digital CCTV Systems for more information.

Those with access to the CJX network can find more system specific information on www.hosdb.pnn.police.uk/cios.htm.

Video recordings are admissible as evidence and the digital storage of these has not altered this. It is of course the courts’ decision whether to accept or decline any evidence, though digital video evidence is routinely accepted in court. It is important to maintain an audit trail while any video evidence is in police custody. Check our publication no. 58/07 - Digital Imaging Procedure for further information.

Image enhancement can uncover information within the image that is not initially evident. Unfortunately CCTV images generally have low information content so any improvement is only marginal at best.

However the following simple enhancement techniques could be beneficial.

• Adjusting the brightness and contrast levels
• Applying sharpening or edge enhancing filters
• Increasing the colour saturation
• Removing noise

More sophisticated image enhancement systems are available, but again their effect is limited on low quality images.

It could be, but rarely is.

• The main potential advantages of digital video are:
• Higher image quality;
• Easy export and duplication of video data;
• Addition of detailed metadata (e.g. time, date camera label etc.);
• More convenient storage options.

However the reality is that:

• Image quality is often low due to poor data compression methods.
• Processes for exporting video data are complicated and generally specific to each manufacturer.
• Metadata use is unstructured and varies between manufacturers.
• Systems are often set to maximise storage which reduces the quality of stored video data.

As with analogue systems, digital CCTV systems need to be correctly specified, installed and properly maintained to gain the maximum benefit.

While the original recording such as the system’s hard disk drives may be seized as master evidence, it is more usual for the original image files to be copied to WORM (Write Once Read Many) media such as non-rewriteable CDs or DVDs. It is from these that working copies can be created.  Check our publication no. 58/07 - Digital Imaging Procedure for more information.

Facial mapping (or facial comparison) is viewing two or more images and determining whether they contain the same person. It is a highly subjective process whereby court recognized experts attempt to prove or disprove identities within a scale of confidence. Other detracting factors include the person’s position, poor lighting and low image quality. As these factors are inherent within CCTV systems the results from facial mapping are often low in confidence or inconclusive.

 

 

Clearly identify your requirements and budget. The main areas to consider are:

• Quality – are the pictures good enough?
• Storage – are the pictures stored appropriately?
• Export – can the pictures be easily exported from the system?
• Playback – can the pictures be easily viewed by authorised third parties?

We  have updated publication 17/94 CCTV Operational Requirements Manual v3.0 with v4.0 publication 55/06 which includes specific advice on digital systems.

Video data from your CCTV system may be required to assist with police investigations. To facilitate this, the Home Office have issued a guidance document 'UK Police Requirements for Digital CCTV Systems' (HOSDB publication number 09/05). This provides advice on how best to make your video data accessible to police officers.