A strategic solution to this problem is to concentrate on capturing high-quality images that will permit facial recognition of each person as they enter and leave the centre. This is particularly useful in allowing 'known' persons to be identified immediately. Less detailed images will then suffice to track persons as they move about the centre, relying on details such as the clothes they are wearing and the bags they are carrying.

Notwithstanding areas of special interest or hot spots, this approach allows CCTV coverage throughout a centre on a sensible budget, while fulfilling the necessity of identifying subjects for evidential purposes.

Unfortunately, capturing good images at entry and exit points isn't necessarily easy. People entering the centre may be lit strongly from behind, putting their faces in shadow. The answer is to use cameras specifically designed for this type of application, able to cope with contrasts between the light and dark parts of the image without losing essential detail.

Capturing good images is the first requirement of a CCTV installation, but the images then need to be recorded. Today, the only realistic option is to use a digital video recorder (DVR). These record the images onto hard disks, similar to those used in computers. Not only do DVRs give much better quality recordings than old-fashioned VHS tape systems, they're also more dependable and much more secure.

There's one point to watch when choosing a DVR. All machines compress the image data from the cameras before recording it on the hard disk, and all compression reduces image quality. If the DVR uses a normal level of compression, the loss in quality is almost undetectable. However, in order to produce a competitive product, some DVR suppliers may use a very high level of compression, and the result will almost certainly be poor quality images. The best advice, therefore, is that if the price looks too good to be true, it probably is.

Another benefit of modern video-analytic systems for shopping centres is the identification of hot spots and quiet spots in terms of customer traffic. This information can be used for marketing campaigns and in the setting of appropriate rents, with those stores in high traffic areas charged proportionately more than those in other areas.

l Alistair Enser is UK sales director for Siemens Building Technologies Security Products

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