This was actually a response of mine to a question on another post, I've decided to expand on some of the points and offer it over for discussion.
My view on CCTV, is that just like anything else the government have brought in, they did it half arsed. It's very good when it's used properly and to it's full potential but without sufficient resources to use it fully in all cases, or to store and use in court proceedings, it is almost worthless most of the time. CCTV can be invaluable in fast time incidents where the control room or an experienced operator can give the officers on the ground not only the information they actually need, but a mental image of the scene prior to arrival. As an eye in the sky, in many cases it beats a plane or chopper hands down with value for money and versatility, but ONLY when used live.
As for trawling through hours and hours of CCTV for incidents it has to be viewed and used in real time and costs hundreds of thousands in man-hours every year, although some of the evidence that can be gleaned can be pivotal and can make or disprove a case. In courts they still demand the CCTV on VHS tape as they haven't got duplex (ability to view lots of camera angles recorded at once) or DVD players because of cost. Most council and private CCTV facilities now store onto hard-drive because it is more cost effective than additional storage or tapes and quicker to access and can burn off easily onto disc. The cost in time alone of transferring to a system that is nearly 30 years old from DVD's to VHS tape, is completely rediculous.
Added to this, is the fact that most police computers have the CD drive locked out to stop people listening to music or uploading software (which they never could or did anyway, as with the internet they blocked access before anyone ever got the chance to abuse it through fear of looking bad in the press or to the public) even viewing CCTV becomes a complete pain in the arse and cannot be done quickly or easily. Virtually all of the time we have to view it at scene in order to get all the information we need for the crime report or to relay to other officers. I also have no idea how many times I've been to a job where the person who knows how to use or even access the system isn't there, or no one actually knows how to use it as the head office just installed it without showing anyone how it works.
It's all well and good bringing in the cameras if you can use them properly and the infrastructure is behind them to actually use them effectively as evidence in court or investigation, but it isn't and in most cases it is collected and stored as unused evidence at the behest of the CPS. In many cases it's collected for negative evidence as the cameras aren't actually that good, it is also collected to cover arses as it is almost certain that somewhere a CCTV camera has seen some part of an incident and even if the footage is worthless, we can't be seen to ignore it.
I have no idea how many people think that CCTV is as good as on TV or in the movies, it categorically is not. In most cases such as shops or some old council cameras the image is shocking, due to poor quality equipment and an unrealistic expectation of its value. CCTV used to be a good deterrent when it first became popular, but nowadays many criminals know that it is practically worthless. They know that their brief will be able to bring the quality into question anyway and also that the chances of every frame of every vid being analysed and watched properly is incredibly slim. Whereas areas that install CCTV see an initial drop in crime, after time the crime rate creeps back up to its existing levels as they simply don't care if they are on camera any more.
There is also no such thing as digital 'zooming' of an image that can be used for everyday investigations, the reason for this is a computer program is used to extrapolate the information in the image to enhance it digitally, which is technically nothing more than an educated guess. An image only contains a certain number of pixels (such as the ratings used to show the resolution of digital cameras) and whether you have 1k pixel images or 10 mega pixels, if you zoom in too much you just end up with a big pixel on the screen. There are systems used by the military and other government agencies however they are not admissible in court. The reason it is not admissible as evidence is because one computer program could give one result and another could give something else and so there develops a question of doubt. Even if the system is proved to be 99.99% accurate, the 0.01% of doubt is an issue a good defence brief would bring up and capitalise on during trial, with the view to getting the evidence deemed inadmissible.
You can use a computer program to clean up an image by clearing static 'snow' pixels or enhancing the colours of existing ones. This type of enhancement was used by the FBI labs in the Milly Dowler case to ID a car, but there is nothing usable in court today of the same level as in the film Blade Runner where they zoom in almost indefinitely to a photo to get an image.
A perfect example of the expectations and limitations of technology is the photos that Police officers took at the 'Jack the Ripper' murders. They photographed the eyes of one of the victims in the hope that in the future the technology might exists to zoom in enough to get an image of the murderer. However due to the resolution of the film and prints, you can't blow up what isn't there in the first place and using a computer program to try just gives an indication, not proof. The same goes for a digital image and a tape frame.
In a case a few years ago, I had traced a car via CCTV through a large part of the city I worked in, from the location of the incident to a few hundred yards away from where the suspect was arrested in the same car as ID'd by the description of his face and the number plate. When I took the 15 odd tapes from the different cameras to the tech guys at HQ they did all the cleaning they could, but I was amazed at how little they were actually able to do to the image through possibility of corrupting the evidence. I learned that even in near darkness they could determine the colour of a car by analyzing the colour reflections from the headlights, but even that was not accurate and only gave a basic indicator such as red, green or blue. I had to use another car of exactly the same model that was luckily parked up at the roadside on one shot to prove the car we were looking at was the same model. As for zooming in and seeing the number plate or even the drivers face; not a chance.
A further problem I faced was the time index on each individual camera was actually different. In order to prove that it was the same car from each camera and not two conveniently placed cars of the same make, model and colour travelling at high speed from the incident I had to work through every camera in real time to get the difference, and then had to do the same to our radio comms channel, the incident log and the Police national computer. Every single clock was different, including the watch on my arm and the only way to get a proper reading was to sit on the phone to the talking clock. Without going through the pains of calculating the differences, which took hours, the CCTV could have been inadmissible through doubt of worth. As investigations go it was extremely interesting and worthwhile in the end; however the question of proportionality to the offence has to be raised. Imagine having to do that for every incident, let alone having to view every tape in real time anyway.
I had a guy recently come into the station to ask advice with regard to damage to his car. It was parked in a bay and he new there was a council camera about 50 meters away that looks at it and wondered if the traffic department would seize the tape and view it to get a picture of the driver. I was honest with him and told him that they probably wouldn't, simply because CCTV is so over rated. Some record at only one frame every second - sometimes every 3 seconds - and the likelihood of actually getting the car, driver and registration number for insurance was incredibly slim. We filled the form out for him anyway, but I had to be realistic that the chances are he would be footing the bill himself unfortunately.
At incidents where you have different accounts of what has gone on you can use recorded CCTV to give an indicator as to who is telling the truth but without sound and live record, it is still not great and you can never get the nuances of body language on one frame a second video footage. There has never been a conviction based solely on CCTV evidence, there has always been some other corroboration so as the governments answer to solving crime it's not all it's hyped up to be. At nearly every incident I attend now we have people saying "the CCTV will prove it, go and watch it now" and to be honest the fact that there is CCTV everywhere (and thanks to TV programs) it gives the public an extremely unrealistic view on its evidential value and potential.
It's a very simple tool in the box, nothing more.