Everything you wanted to know ...

Q: Digital recorders cost far more than VCRs and multiplexers – how can I justify the additional cost to end users?
GJ: In most cases digital recording is no longer the extremely costly option it used to be, although this does depend on the storage time required and the number of cameras involved. However, it does cost more to provide a digital system and the installer has to be able to justify the added expense to the end-user by focusing on the benefits offered. These can be summarised as:

a. Higher recorded picture quality
b. Faster picture update rates (usually measured in images per second)
c. Instant access to recordings (can be dependant on the type of recorder)
d. Enhanced compliance to data protection legislation
e. Lower maintenance costs

Q: What do these advantages really mean in practice?
GJ: Higher picture quality and faster update rates combine to make the recordings far easier to gauge what has actually happened in the scene. The playback is much smoother that a normal VCR/Mux setup and there is no tearing and jittering which happens with a freeze frame image in a video tape. The result is that the recordings are of more use to everyone, a huge benefit which is often overlooked.

A good digital recorder will not have to rely on expensive and cumbersome tapes to store and back up the images – all the recordings should be stored in the machine. The user should not have to worry about where the recordings are stored. Recordings made last week should be as easily accessible as those recorded two minutes ago, without having to find last week's tape, plug it in and then wind backwards and forwards to find what you're looking for.

In practice, the amazingly short time it takes to find incidents with a well-designed all-hard-disk digital system makes it feasible to produce evidence for even the smallest incidents. With video tapes (or even with tape-based digital systems), it is simply sometimes not worth the time and effort needed to find the recordings.

Q: How does the user actually provide images from the system when evidence of a crime is needed for the police?
GJ: Obviously this could be the subject of an entire article. Clearly, any CCTV recording system that can't export evidence is about as much use as the proverbial chocolate soldering iron. Every digital recording system on sale looks like it can export evidence when you read the specification sheet, but the medium used for this needs to be viewed in the context of what an "officer dealing" can actually use.

Exporting of evidence is probably the most telling area of comparison between different DVRs but I would go further and argue that this should also form the benchmark for comparison between the old VCR technology and digital recording.

The fact is that despite the obvious faults and operational difficulties inherent with VHS video tapes, they have one significant plus point – everyone can play them (assuming they have a compatible multiplexer).

Q: Surely then a DVR should emulate this principle and provide images which have all the aforementioned advantages of digital technology (image quality, fast update rates etc) and can be accessed by anyone?
GJ: I have to declare an interest here and advise that I work for a digital recorder manufacturer that has a particular view in this area, so to an extent I'm doing my job. But I will point out that recorded images exported from our systems have been used many times in court with positive results. Here's how. We export to CDs, which are cheap and convenient. Also, most police stations are equipped with at least one PC (pardon the pun). The idea is that the officer issued with the CD can pop it into his machine and look at the images without the need for any specialist equipment or software – just like a video tape.

Q: What happens when a really serious incident takes place and the police want to seize the recorder?
GJ: Frankly, this is digital recording with its knickers down. CCTV folklore is littered with stories of DVRs being taken away as part of an investigation. The reasons for this are probably split equally between the natural caution an officer will show towards unfamiliar technology that's involved in a serious incident and the DVR manufacturer's inability to make a "real world" evidence handling system. Exporting to CD, DVD, Jazz, Zipp, DAT or anything else is fine as long as a) it can be read by the police, and b) they don't need days and days worth of images. If the latter is the case, be prepared for the kit to disappear into the boot of a panda.

There are ways to avoid the worst happening.

At Visimetrics we've developed a "first best evidence" image protection feature which locks original recordings permanently on the hard drives (see Home Office Science & Technology Committee's "Fifth Report" on Digital Images as Evidence). Once protected, copies of the original recordings can be made as required. The probity of these images as evidence is maintained, because you can show a clear audit trail to the original.

Q: What about audit trailing, watermarking and security in general?
GJ: I think its probably true to say that to an extent, all DVR manufacturers are staggered by the hoops we have to jump through in these areas. Just indulge me here for a moment and consider how secure a traditional VCR system is (or not).

For a start, there are no log-ins or passwords required to start, stop, rewind or fast forward a VCR and even more scary, anyone can remove a tape. Lets think about that tape a bit more – it's a standard domestic type item so could be replaced without anyone suspecting a thing. Add to this the fact that multiplexers don't have any real security either. Hopefully you can see what I'm driving at. In summary, there is absolutely no security whatsoever associated with the technology we've all been using for as long as anyone can remember, yet its validity is never questioned despite its poor quality.

A digital recorder with no passwording, audit trail or encryption is probably ten times more secure than a traditional system. However, the technology exists within the platform of most digital recorders to dramatically increase security and so naturally this is implemented. Most DVRs will provide a log-in/passwording system and data security, although the Home Office Science and Technology Committee's Fifth Report states that the latter is not required for evidential purposes.

All this means that the security of the images and therefore their evidential value should be very high, given how insecure it's all been up until now. Still, you can't overcome the natural human resistance to new things overnight, even if they are better…

Q: What about compliance with the Data Protection Act using digital recording?
GJ: Data Protection legislation affects the whole CCTV system but it's fair to say that the recording method probably has a greater effect than any other sub system on the compliance (or otherwise) of the whole installation.

Happily for all of us involved with or using digital recorders, compliance to many of the principles of the Act are automatically ensured. These include- "The medium on which the images have been recorded should not be used when it has become apparent that the quality of the images has deteriorated".

This is the part of the DPA which is really telling you to be a responsible operator and make sure your tapes are of good quality, clean and erased before each use. It relates to the Third Data Protection principle. A proper DVR system shouldn't use any tapes at all so users don't have to do anything (especially involving time and money) to comply with this aspect of the law.

"Users should assess whether it is necessary to carry out constant … recording or whether the activities …occur at specific times."

This little gem (which comes out of the First and Third Data Protection principles) really exposes one of the fundamental differences between the old analogue systems and DVR. Instead of just recording everything that happens all day and all night, DVRs can be programmed to only record from specific cameras at specific times, or even more usefully to only record when they sense motion. It is worth mentioning at this point that apart from automatically keeping you legal, this also means you can tailor the storage capacity to the site's requirements. As a further bonus, it's even easier to find incidents because the recorder will highlight the events.

"Images should not be recorded for longer than is necessary"

This rule exists because of the Fifth Data Protection principle and again puts digital recording in a very advantageous position. Because they automatically overwrite, there is, yet again, no user input required to stay on the right side of the law. The whole area of image "archive" time can get quite contentious. As hard drives have got both larger and cheaper it has become easier to provide longer and longer archive times. Visimetrics currently fit just over a Terabyte (1,000Gb) into a single desktop machine and obviously we're very happy to supply these. However it is questionable whether users actually need such long archive times. The law has a view on maximum recommended recording times and users should bear in mind that the important word here is maximum. Just because the local CPO has said that keeping 31 days archive is "the law" does not make it true.

Q: "Upon making a request in writing … an individual is entitled to be told … of all the information …by way of a copy"
GJ: Our experience so far in talking to users is that the feared tidal wave of subject access rights requests from the great unwashed has not materialised. However, if and when it does, digital users will be in a far stronger position yet again. There are many easy and cost effective methods of providing data to third parties for reasons other than evidence handling, and printing (via a standard printer) or copying to CD will be faster and cheaper than with tape-based systems.

Q: How do the different compression methods such as JPEG, MJPEG, Wavelet etc affect recorder performance?
GJ: Yet another area of the technology which warrants a separate article all of its own. All digital video recorders have to apply some sort of compression to the images in order to fit the pictures onto the drives and the method used often causes a great debate. Our view is that there is no right or wrong method but that in general, so-called conditional-refresh methods (e.g. MPEG, H261) will not produce as good an image quality. For this reason, some recorders appear to require far less hard disk capacity than others to achieve the same archive time.

Again its important that I declare my own interest here and point out that at Visimetrics we use JPEG compression, because we feel this gives the highest quality and is one of the most evidentially robust methods available.