The issue of digital images as evidence is in focus as this new
technology takes off in the security world. Demand for digital is
rising rapidly as the cost of commercial applications falls
(particularly for storage and maintenance). The quality of digital
technology is clear to see quite literally with superior images that
are more flexible to store and transfer.
So what is the difference between traditional analogue video
images and images obtained from digital surveillance technology - and
why all the fuss?
Analogue
Traditional analogue Images are recorded in some physical form, such
as frequency, amplitude or in the case of a photograph, the activation
of photo-chemical emulsion.
Digital
A digital Image is recorded as a series of binary digits (called
bits) - either ones or zeroes. The image is then focused onto an
electronic sensor comprising individual light-sensitive elements known
as pixels (picture elements). These act as switches to modify an
electrical current on or off and the information is processed by a
computer. It can then be displayed on a screen, stored in a variety of
media or printed out.
The Select Committee Report, 'Digital Images and Evidence', seeks to
clarify the difference (see panel above) and makes recommendations to
the Government on the way forward with digital CCTV images. For a
court, the key word is 'traceability' - having a cast-iron audit trail
that takes you right back to the original recording. This means that
whatever happens to an image if it is enlarged, printed out, even
tampered with - the original remains for a court to examine. Because
digital technology is so new, people are having to get to grips with
the fact that a digital image consists of a series of ones and noughts
that are converted by a computer into an electronic image. But that
doesn't mean they should be any less valid than a traditional analogue
image.
Far from saying digital images cannot be used as evidence the
Report lays out guidelines about ensuring their authenticity. Like
analogue images, suitable procedures should be followed in collecting
and monitoring what is captured on camera. Indeed, the Select Committee
established that digital images have already been used as evidence in
court. For example, images from a system installed in the car parks at
Heathrow Airport have been successfully used as evidence.
It seems certain that the increasing popularity of digital
technology coupled with the fact that images can be replayed countless
times with no diminution in quality means its widespread use and
acceptance as evidence is inevitable. Analogue or digital images are
unlikely to be the only evidence presented in a court case. In fact,
they are far more likely to be used before a trial to make a person
admit their involvement in a situation.
From our understanding of the Report, the Government is saying
that methods of storage and authentication of surveillance images
should continue as before. Many of the issues created by new digital
technology will be governed by the new Data Protection Act.
The Data Protection Act is significant because unlike analogue
images, digital images are covered by the Act. This seeks to protect
individuals from the use of personal information without their consent,
such as their names and addresses. It is very detailed about the way
data must be handled and stored. By falling within the remit of the
Act, digital recordings are therefore governed by very stringent
guidelines and controls.
What is important is that end users of digital surveillance
equipment know what is expected of them in terms of the way they
record, store and use digital images. It's not so much installers but
the impact on their customers that need to be considered. Installers
should make sure their customers know what is expected of them.
We're helped here by a number of specific recommendations made
by the Select Committee and endorsed in the Government's official
response. Digital technology has the capacity for encryption and
security coding so some kind of electronic audit trail involving file
coding of digital images is suggested. A permanent physical record of
the data that cannot be amended is one idea - this could be some form
of write-once read many times' (WORMS) disk. Creating an audit trail
would reduce the chances of undetected tampering of images.
These are some of the main Report recommendations which the
Government has said it hopes will help to form 'best practice' in the
security industry and elsewhere:
- Responsibility for proving the reliability and authenticity of
data is with the body that captures, processes and modifies it. A
suitable audit trail is essential
- Where digital images are considered as evidence, courts
should place greater weight on evidence that can be shown to be derived
from an authenticated original. Juries should be informed of anything
to doubt the authenticity of digital images
- As with analogue images, proper records must be maintained
showing who was in control of the equipment at the time of an incident
and subsequently in charge of any images created, and who is
responsible for the storage and retrieval of those images
- The Data Protection Act 1998 should provide the regulatory
framework to cover CCTV-derived images, including digital data. The
Government supports the idea of devising some kind of incentive such as
endorsing codes of good practice that are based on the quality,
integrity and authenticity of data. Factors here might include:
- The way in which systems are tested, including on-site, by installers or users
- The way systems are set up, calibrated and maintained
- Environmental conditions
- Operating procedures
- Training of users
- Automatic quality warnings
What installers need to make their customers aware of is not just
the fact that digital and analogue images differ but to ensure that the
same careful approach is taken to the way any image is captured, stored
and maintained. They need to make sure their customers understand the
importance of ensuring traceability of surveillance images.
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