A: You're not alone! I've heard a few tales from installers about units being confiscated.
Fortunately there are a number of ways to get the images off the DVR without having to hand the unit over. The main issue with copied images is that there must be some method of proving that that they're from the unit in question, and that they haven't been tampered with irrespective of the archive media used. The application of a digital signature makes it possible to detect whether a single image or sequence of images have been tampered with, and also provides the date, time and ID of the unit recorded on.
I'll begin by giving a brief outline of what archive methods are available. Then an overview of standards that archived digital images should attain when provided as evidence to the courts, according to suggested guidelines jointly drafted by the Police Scientific Development Branch (PSDB) and the cross-industry Digital Forum.
CD-ROM archiving
CD-R compact disks are the most suitable archive medium when a short video-sequence needs to be transferred. They have the added attractions of being very reasonably priced, and robust – unlike the traditional VH-S tape! And, as such, they are a universally accepted data storage mechanism available in virtually every modern PC.
These disks typically have a storage capacity of around 650MB. At 6 PPS (pictures per second) you'll be able to store approximately 1 hour and 36 minutes of recording compressed to an 18KB file size – assuming all cameras are recording of course. If the record rate was set fairly high at 25 PPS for example, 23 minutes of video data could then be stored to disk.
A copy of the manufacturer's playback software should be supplied in each image sequence directory, and images stored on the CD-ROM must auto-run directly from the disk. No additional software installation should be required to facilitate playback of an image sequence.
Bulk file export
Quite a number of manufacturers offer a high-speed interface to their equipment. These consist of SCSI port, standard ethernet port, Firewire, and USB ports.
With the exception of SCSI, all of the aforementioned data transfer methods export files over a network to another computer with sufficient storage capacity. Bulk downloads need to take place in a secure area – for example the control room – and preferably witnessed by a member of the police. Data transferred whilst witnessed would constitute "best evidence".
If SCSI is employed as the archive method, then suitable external archive devices will need to be employed with sufficient capacity. For example, a 2GB JAZ drive will record approximately 2 hours worth of recording at 6 PPS compressed at 18KB, or 1 hour and 12 minutes at 25PPS.
It's important to ensure that the digital recorder continues to record with no loss of performance, whilst background archiving takes place. Not much use to the end-user if recording has to stop to preserve the integrity of the images being stored!
DVD archive options
There are currently two options available: DVD-R recordable disks and DVD-Ram writers. DVD-R can only be written to once and remain prohibitively expensive. DVD-Ram on the other hand, whilst still costly in comparison to the CD-R, can be written to many times over.
In the longer-term, as the costs fall and hardware becomes more widely used, they will probably provide the most appropriate solution for larger storage requirements – offering around 4.6 GB per side.
Digital images as evidence
The first thing to note is that there is no specific legislation which expressly covers digital evidence, it is treated the same as computer records which is covered by the Police and Criminal Evidence Act 1984. However the House of Lords Science and Technology – Fifth report, (Session 1997-1998) does find that digital images are admissible as evidence in UK courts of Law.
When it comes to providing the police with digital images as evidence the main issue is not then whether they'll be accepted, but on proving the authenticity of digital images – which is much the same way as with any form of evidence, i.e., how it was produced, how has it been controlled and its origin.
The report finds that proving authenticity of digital images is, in fact, much easier and can be proved more scientifically than with traditional VCR based systems.
Digital images can be authenticated using established digital signature techniques to verify the authenticity of images.
According to draft guidelines drawn up by the Digital Forum and PSDB each image sequence directory should contain header data that includes, amongst other things, the camera and unit details, the date and time of the recording (according to the date/time settings of the unit) and an incremental sequence number.
Archived to CD
If the images are then archived to CD, DVD or bulk exported, the digital signature should then be recalculated and reapplied using the header data and the whole of the image data. As images and files are copied to the file then further digital signatures are generated culminating in a single signature that can be applied to the whole of the archive media and is recorded in the header area of the file.
The upshot of this is that the final digital signature applied to the archiving media can be used to verify that the entire contents of the file are as originally recorded right down to the individual bit levels within images.
Backup copies can be made and can be verified, but these must be image copies of the original as file-by-file copies will not generate the same digital signature. The image viewer software transferred to the file with the images can be used to fully verify the contents of the file.
I've only been able to give a brief overview here of the archive options available and judicial guidelines concerning digital images.
For further information you can find the House of Lords report at http://www.parliament.the-stationery-office.co.uk or contact the PSDB through their website http://www.homeoffice.gov.uk/pcrg/psdb.
Source
Security Installer
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