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The big picture with images for evidence

One of the key motivations for investing in a CCTV system is to provide images of sufficient quality to assist in investigating and prosecuting people involved in criminal activities – which could range from in-house shrinkage and shoplifting to armed robbery and other violent crimes. So factors that influence image quality (IQ) have to be carefully considered.

One of the issues with using CCTV images for evidential purposes is that users are not aware of all the technical issues involved with using CCTV images for evidential purposes.

The recent CCTV white paper, published by Consumer Goods Council's Crime of South Africa's (CGCSA) Crime Prevention Programme, has set out to address this situation by producing a clear set of standards that is based on international law and best practice.

One of the key messages contained in the paper is the importance of understanding and differentiating between the different levels of performance that CCTV systems can offer. Performance levels start at monitoring and climb up through detection and recognition before reaching evidential levels at identification. There is a separate category for reading licence plates on vehicles.

The identification level where 'picture quality and details need to be sufficient to enable the identity of a subject to be established beyond reasonable doubt', is the only one that would be considered as 'sufficient for identification to be made based on the images alone'.

The images should also:

* Clearly show the actions of persons involved in the incident.

* Give evidence of the identity of offenders and victims where appropriate.

* Show an overall view of the scene.

* Be date and time stamped with verified date and time.

So it becomes obvious that, if one is hoping to use the recorded images to assist in a conviction, the equipment and other factors influencing the quality of the images will be required to meet high standards. Each component of a CCTV system has a contribution to make towards achieving the goal. (For more on the legal side see 'Proving the point: CCTV as evidence').

Special attention needs to be given to camera specification, numbers and placement. Low-end cameras are unlikely to provide worthwhile images - high resolution and varifocal lens are required. Access points will need two cameras placed no higher than 1,6 m to record faces hidden under caps and care needs to be taken to ensure cameras are not obscured by displays or boxes etc. Cameras can also be attacked or disabled by a variety of substances or devices so it is important that more than one camera can view each area and care should be with placement to try and keep the lens out of harm's way.

Requirements for quality signal transmission need to be carefully assessed at the design stage as distances involved may require a higher-specification cable and amplification of the signal may be required for cables longer than 300 m. Although it is tempting to skimp on the 'additional extras', a lack of adequate lightning and surge protection will only prove the maxim: 'cheap is expensive'.

Similarly, the temptation to use television screens instead of proper monitors should also be resisted. It is hard enough with the best screens available for control room personnel to remain focused on screen activity for long periods of time without adding unnecessary eyestrain into the equation.

One point to watch out for with digital video recorders (DVRs) is to ensure that there is a simple, straightforward and robust method of taking recordings off the DVR for evidential purposes. Although this is one of the most important features of a DVR, it is surprising how often this can be difficult to achieve. Whatever method is employed, it should be thoroughly understood and approved by the user before purchase.

Another surprising challenge in this well-established technology can be ease of use so it is worth taking some extra care to ensure the recorder is going to perform to the expectations and capabilities of control room personnel. Competition between manufacturers trying to differentiate their products can sometimes muddy the waters from a user's point of view.

Of course the blindingly obvious also needs to be taken into account: how easy is it to switch off the power, rendering the system useless? And are you organised for unplanned outages? Criminals are always looking for the easy or unplanned opportunity so even the most sophisticated system still requires protection.

And here is a final thought on operations: the tendency to focus on higher-risk groups, such a male teenagers, should be balanced by the fact that anyone - even little old ladies - can sometimes represent a threat.

The CGC white paper offers a number of equipment guidelines at the identification level.

Cameras

* Cameras must produce colour images.

* Monitored access doors must be fitted with cameras which enable clear, unobstructed images of all persons entering and exiting the premises.

* Where practical, cameras should be mounted internally and positioned facing towards the door rather than down at the doorway.

* Cameras must have a minimum of 400TVL (or better than 600 x 450 pixels) resolution.

* Where covering a large area, cameras should have pan, tilt and zoom (PTZ) features.

* At the identification level, if the size of the viewing screen is considered 100%, the size of the image (based on an average 1,6 m person) for identifying people must exceed 120% and for licence plates the image must exceed 50%. Oosthuizen comments: "Zoom control is therefore an important feature as is the placement of the camera."

Transmission

* The system should be capable of 25 frames per second recording levels where there are high levels of movement.

* Wireless transmission is not recommended as it can be easily jammed.

* If compression is used to reduce bandwidth requirements it must produce response times capable of observing any incident.

* Image quality needs to be preserved between source and destination devices.

* Lightning protection is recommended at all entry points to the recoding system.

Display

* Colour monitors are recommended.

* A minimum of 500TVL or better than 750x560 pixels is required.

* Normal television screens are not recommended for image quality and ergonomic reasons.

Recorders

* Time and date stamps must be recorded with the image. These need to be maintained and synchronised across the entire system.

* There is no legal requirement for watermarking so it is deemed to be unnecessary.

* Backup of recordings is important and needs to be properly indexed and catalogued.

* Recording must indicate the camera that generated the images.

* The system must allow for simultaneous recording and playback without any interruption.

* Images should be digitally recorded onto a hard disk.

* There must be a means of transferring these stored images into formats that the SAPS can use - the default software of either Windows or Mac operating systems is acceptable. Exported images must maintain original quality and be protected until exported.

* Retention periods for recording should be capable of being changed.

Playback

* The software should offer variable speed control, frame-by-frame and reverse features as standard.

* The software should display single and multiple cameras and maintain relative height and width.

* The software should find recordings by date and time or change in a selected area.

The information given here is extracted from the CCTV White Paper with the kind permission of the Consumer Goods Council of South Africa Crime Prevention Programme. Copies of this paper are available from [email protected].

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