The weakest link!

This figure is very high, and further investiga-tion revealed that because many end users had not yet had to present footage captured by a digital system as evidence, they were unfamiliar with the correct procedures which need to be followed to ensure footage is acceptable in a court of law. When further questioned, some end users revealed that they were aware of the procedures to present footage from an analogue system as evidence, but had yet to consider the difference when dealing with digital data.

Since their introduction to the security industry, one of the main selling points of DVRs has been that there is no longer a need for operators to remember to change the tape every day! This might be true, but the reality is that digital video footage is memory-intensive.

If a DVR is recording 24 hours a day, even with a number of video inputs being multiplexed, the HDD is going to become filled very quickly. Unless footage is recorded on an event basis, or at very low frame rates with the lowest quality settings, vital footage could be lost.

It is frightening to think that in a worst-case scenario, this means that three out of every five digital CCTV systems might, if challenged, have their footage ruled as inadmissible for evidential purposes. In reality, that means the CCTV system could turn out to be next to useless!

Digital Video as Evidence
Given that the number of digital-based CCTV systems are on the rise, it is a worrying fact that 66 per cent of users with such solutions, according to independent research, are unsure of how to present video footage as evidence. It is worth noting that of those asked, a significant number were aware of evidential procedures for analogue-based footage.

Digital CCTV is increasingly being used by end users, and this trend is unlikely to change. As a wider range of product becomes available, costs will inevitably fall. As use of digital options increases within the market-place, the benefits associated with the emerging technologies will be acknowledged more widely, and the future will see consistent growth levels in the CCTV sector. Whilst this is obviously good news for the installer, it does mean that some end users will have to go through something of a learning curve when systems are upgraded.

It is vital that security installers working in this sector ensure that end users are fully conversant with the procedures for presenting digital video footage to the police for evidential purposes. The correct procedures are outlined in a document published by the Police Scientific Development Branch. The document – Digital Imaging Procedures (Version 1.0) – specifies how evidential footage must be copied, handled and presented for use in a court of law. All installers offering digital-based solutions should have a good working knowledge of this document, and must ensure that end users understand the procedures to make certain that footage is admissible.

Whilst analogue CCTV systems produce a single copy of any footage (in effect the tape is the original), digital systems store the actual captured data in the machine's internal memory (the exception being digital tape recorders, which like their analogue counterparts produce one removable copy of footage). The courts recognise that digital devices are capable of producing 'bit for bit' copies which contain identical data. Therefore, when a video sequence is required for evidential purposes, a Master Copy needs to be made. This should be taken directly from the hard drive of the machine and, once archived, no further data should be added to it. It should then be kept securely.

WORM is an acronym for Write Once, Read Many. Examples of WORM media include the CD-R and DVD-R. These storage devices can have data written onto them once, and once 'closed' (i.e. the writing process is completed and terminated) the data stored on them cannot be altered, deleted or added to. However, the data can be 'read' many times, or in the case of digital CCTV footage, viewed many times.

The insistence on the Master Copy being stored on WORM media is so that after the event, tampering cannot take place, nor can any additional data be added. Where images are transferred from the DVR on a reusable medium such as a memory stick, ZIP disk or other device, they should then be transferred to WORM media. It is vital that once the Master Copy is made, the images on the DVR are not deleted without authority.

Digital video offers big advantages to end users but it is vital that installers ensure end users are fully conversant with evidential procedures.

The Master Copy, as stated earlier, should be stored securely. For the purposes of on-going investigations and preparing the case for court, Working Copies will need to be produced.

Working Copies can be made in one of three ways. They can be made simultaneously with a Master Copy when a system supports writing numerous archives to WORM devices at the same time. Alternatively, they can be made from the original recording subsequently to the Master Copy being created. Finally, Working Copies can be made as direct replications of the Master Copy. However, Working Copies cannot be made from other Working Copies.

When creating the Master Copy, there are certain elements which the media must contain. Installers should ensure that end users are well aware of this requirement, as once a Master Copy has been created data cannot be added at a later time! The Master Copy should include the video sequence or sequence of images, and these must be clearly identified. Any associated data such as time and date information should be bound to the images. The footage must be accompanied by a text file which outlines the requirements for hardware and software to replay the footage, as well as licence-free software which allows the video footage to be replayed and copied, and permits the creation of editable copies too. Finally, the Master Copy should also include instructions for transferring the video footage to a VHS tape, additionally highlighting any differences which may occur if a VHS version is played alongside a digital version. This latter requirement might seem a little regressive, but it has to be remembered that the majority of courts and police facilities are equipped with analogue-based systems, and until digital systems become the norm in such establishments, this requirement will stay in force.

The Master Copy can include a text file copy of the audit trail, and information about the cameras and system if required. A test sequence to show correct operation of the review software can also be included. However, none of these items are mandatory. Another element which can be included, but again is not mandatory, is some form of image authentication or verification software. There is some confusion about this issue, with some experts stating that authentica-tion such as watermarking, Checksum Algorithms or encryption are required. They are not, although such measures do highlight authenticity should a challenge be made on the basis that the video footage has been tampered with!

Digital Archiving
The DVR has many benefits, and the introduction of these next-generation devices has certainly advanced the options available when looking to design a system which utilises CCTV recording. However, whilst they do boast integral storage facilities, off-machine archiving is still a necessary and vital task.

Fujifilm's commissioned independent research showed that 61 per cent of end users with digital systems allowed older footage to be automatically overwritten when the hard disk was filled. Such an approach could potentially lead to valuable and required footage being overwritten.

When selecting a DVR, one of the specifica- tions many security installers look for is the amount of integral storage. Given that the average size of a hard drive in a mainstream entry-level unit is between 40 and 80GB, there are obviously limitations on what can be archived, and for how long. As every system will be different in terms of how it is configured, there is no easy formula to work out how much data you can store, despite the assertions of some! Digital image file sizes are affected by a number of criteria. These include image quality, resolution, frame rates, compression method, compression ratio, etc..

Even the content of a surveyed scene can have an effect. For example, images of a shopping mall will be larger than images of an open area in a depot, because of the level of detail contained. Images of a site on a rainy day could even be larger than images of the same site on a clear day! You will often see quoted sizes for image files, and although these may seem low, they can be taken from files with the lowest resolution setting, the highest compression ratio and include test content which has very little detail. Once in the field, a hard disk could be filled in a matter of days if the machine is used constantly.

This means that by the end of a bank holiday weekend, some systems could already be overwriting data which has not been assessed. Admittedly, in larger systems with higher camera counts, systems can be specified with internal storage in hundreds of Gigabytes, as well as Terabytes, but the required recording ability of the system is usually required to be much higher in such applications. In short, allowing drives to automatically overwrite when filled is certainly not best practice, and could lead to vital evidence being lost.

There are a number of options when it comes to archiving digital CCTV images, and by far the most preferable is to use some form of off-machine archiving. This allows footage to be stored securely, correctly managed and audited, thereby also helping compliance with the Data Protection Act.

There are three main choices when it comes to off-machine archiving media. There are other options in the market-place, but these are not suited to CCTV archiving, in that they are either unreliable for long-term storage, cannot support the capacity required from video footage, are considered obsolete or are less than practical because of the cost or availability of compatible drives. As a result, Fujifilm recommends the use of CDs, DVDs or professional digital tape products.

Efficient archiving
Fujifilm is dedicated to offering the CCTV industry credible, reliable and efficient digital archiving media to ensure that important footage is kept safely and securely. Many of the initiatives established in the analogue sector will also be available for installers of digital systems, such as CCTV log books, evidence bags, audit trail support tools and other supplementary items.