If the news is anything to judge by, then England is the CCTV capital of the world. Here are some comments about CCTV best practice from the Cambridgeshire Police Authority.
If surveillance is required 24 hours a day then numerous tests will need to be carried out as regards the lighting conditions that are present and the effects that this has upon the video capture quality. It is often necessary to use artificial light in dark or dusk environments so that any footage captured in this period is distinguishable. It is possible to install infrared systems, however, these can often be more expensive and less effective than the footage offered by a standard system with appropriate lighting.
A CCTV camera may be either, static or mobile in its field of view, both being advantageous in different scenarios. If a system is established to just monitor a specific area it may be better to employ a static system, as the required surveillance area remains prominent. Static cameras may also be preferable on grounds of ease of use, cost and reliability.
Mobile cameras (Some times referred to as Pan, Tilt and Zoom or PTZ) are much more effective when used in a monitored environment. One of the main advantages of mobile cameras is their ability to cover a much larger area than that offered by a static camera. These cameras can also be beneficial when used to track offender’s movements after an event. A disadvantage to using mobile cameras is the fact that they are more expensive initially than a static system and if exposed to outdoor weather extremes then they may need to be sufficiently weatherproofed and must be serviced regularly.
Often in the case of big businesses it can be cost effective to install a mixture of static and mobile systems ensuring that all areas are covered appropriately.
Monitors for a CCTV system need to be based in a secure designated area and must not be open to unauthorised viewing. Monitors can be set up so that they alternate various camera views over a time frame. However, it is often better to employ a few monitors within the system or have a system whereby a camera display will be activated with an alarm or detection system. This will allow you to dismiss a false alarm or to verify an intruder quickly. The recommended viewing distance for operators is 5 times the monitor diagonal. It is also recommended that the number of images that are being viewed on each screen should be no greater than 4. Remember also that target detection decreases as the number of screens to be observed increases. CCTV Operators should be suitably recruited and trained and good working practices, such as regular breaks should be introduced. Alternatively it may be suitable to use a 3rd party 24 hour control room facility.
It is essential that when a system is established then the image quality offered must be good enough for the purpose intended. If the system is installed to prevent and detect crime then the system must reflect that and offer an output quality that can identify an offender or the scene of the crime. Decide if the camera output is intended to monitor, detect, recognise or identify an intruder, This can be expressed as the proportion of the target to be viewed (%).
An observer can observe the number, direction and speed of movement of people whose presence is known to them, i.e. they do not have to be searched for. Subject matter should fill no less than 5% of the screen.
Following an alert an observer can, after a search, ascertain with a high degree of certainty whether or not a person is visible in the pictures displayed to them. Subject matter should fill no less than 10% of the screen.
Viewers can say with a high degree of certainty whether or not the individual shown is the same as someone they have seen before. Subject matter should fill no less than 50% of the screen.
Picture quality and detail should be sufficient to enable the identity of a subject to be established beyond reasonable doubt. Subject matter should be no less than 120% of the screen.
Before purchasing equipment to store footage from CCTV systems, it is essential to consider what the system is being used for and then ascertain which recorder should be used. Three systems exist to record footage, these being “real time”, “time lapse” and “loop framestore” systems. Real time systems offer the best quality option yet they may need frequent exchanging of tapes or may fill memory quicker. Time lapse systems record periodically rather than continuously, this interval can be set from a fraction of a second to a few minutes. Some systems are capable of being manually switched to real time from time lapse. Loop framestores can be used with other detection systems, they record onto a timed loop, the oldest image being re-written with the newest. If an alarm operates the loop stops and the operator is presented with pre and post incident images to verify the incident and decide on the course of action.
Another option for consideration is the introduction into the system of a “Multiplexer”, this can sequentially incorporate several camera outputs into a single video signal, allowing for each one to be recovered. But remember if used in conjunction with a time lapse machine you may be reducing the amount of information or evidence you can recover at a later stage.