House of Lords - Science and Technology

Select Committee on Science and Technology Fifth Report

FIFTH REPORT

3 February 1998

By the Select Committee appointed to consider Science and Technology.

ORDERED TO REPORT

DIGITAL IMAGES AS EVIDENCE

1.1 The tabloid at the supermarket check-out may have another "Elvis is Alive" story with a picture of him holding the last month's issue: inside there might be a story about a World War II Lancaster bomber landing on the moon, with photographs to prove it. But by and large people do not believe these photographs however real they look, and it is doubtful if the authors expect them to. So why should people doubt the photographs in a broadsheet of the Chancellor of the Exchequer holding up his red box on Budget Day in front of No. 11 (The Guardian 3 July 1997)[1]? Even those who approach what is written with a reasonable degree of scepticism have a general presumption that a photograph is what it purports to be. Further, if a jury in a criminal case is shown by the prosecution a clear and unambiguous photograph of the defendant caught in the act, in the absence of any other evidence, will the members regard it with just the same degree of scepticism as they had for the picture of the Lancaster on the moon? And should they?

1.2 Questions such as these led the Committee to embark on its study of the use of digital images as evidence (see Box 1 for background information on images). What initially seemed likely to be a short enquiry into an apparently straightforward and well contained topic was found to be far less constrained. The ubiquity of digital technology meant the subject broadened from images, typically photographs, to closed circuit television (CCTV) on the one hand and databanks on the other. Digital technology has a pervasive influence on many apparently unrelated aspects of society, which was one of the reasons why in our previous report "The Information Society: Agenda for Action in the UK"[2] we recommended that the Government take a holistic approach by setting up an Information Society Task Force to identify the barriers to the development of the Information Society in the United Kingdom and to recommend appropriate remedies.

Box 1: What is an image? Some definitions

Analogue images

The traditional image captured by photography is an analogue image. The images are recorded as a variation in some physical property, for example frequency, amplitude, or activation state of a photochemical emulsion (of colour dyes and silver halides, for example, as a transparency or a negative). This varies with the brightness, colour and contrast of the scene being recorded.

Digital images

A digital image is a numerical representation recorded simply as a series of binary digits (bits): either one or zero with no values in between. The image is captured by being focused onto an electronic sensor (a charge coupled device, CCD) which is made up of individual light-sensitive elements called pixels (picture elements). These act as switches modifying an electrical current on or off and the information is processed by a computer. Images may be either moving or still, the data can be stored on a variety of media (eg compact disc, computer hard disk, or digital tape), and the image may be displayed either on an electronic display (computer monitor, TV screen or computer projection) or as a hard-copy print.

Image resolution

The quality of a digital image depends on the number of sensor pixels and the size of the image as it is displayed. High resolution digital cameras on general sale at the moment have 'million pixel' sensors 1,152 x 864 pixels, (eg the Kodak DC210 for around £650) which will produce a standard five inch by three and three quarter inch photo with a resolution of 115 dots per inch. Compared to an analogue print of the same size, this sort of resolution is very poor but is suitable for displaying on a computer screen. Higher resolution sensors are available and it is likely that they will become more widely available in the near future. Much higher resolution is also available from computer scanners which can be used to digitise paper documents and analogue photographs. Epson, for example, sell a 2,400 dots per inch scanner for just over £500. If linked to their 1,440 dots per inch colour laser printer (for around £200), this can produce a photo-quality hard copy.

1.3 Although there is a common technological link between the many different issues raised by digital imaging, their apparent diversity makes it difficult to draw a common theme for this report. For example, the discussion of CCTV and city centre surveillance would not be complete without reference to the issues raised for individual privacy. But while an examination of the principles behind the moves towards a law of privacy is clearly not part of the remit we have set ourselves, an analysis of the implications for the individual created by the application of new technology, and hence the willingness of the public to accept it, is. Similarly when considering the implications of documentary data we found ourselves looking at the Data Protection Act. Again, with proposed legislation underway it is not our intent to comment on the Data Protection Act[3]. Nonetheless, digital imaging technology has broad implications here for the way we run our society which we cannot ignore. We have taken the initial focus of our study-the digital image, typically in the form of a photograph-and looked at the two adjacent topics: moving images (videos and CCTV) and images of text, either written or as 'pictures' that exist only as data on a computer. All forms of evidence can raise questions of authenticity: digital images are not unique in this respect. For example, questions of forgery arise with more conventional technology. But digital technology raises its own sort of issues and these are the subject of this Report. First we describe some of the ways in which imaging technologies are being used today.

Traffic control

1.4 Most roadside traffic enforcement cameras monitoring speeding offences and red light violations record the image of the offending vehicle onto photographic film which has to be stored at the roadside. This presents a series of problems: the film needs to be kept secure, the film needs to be changed often, the number of incidents recorded is limited by the film capacity, each film needs to be collected and taken for processing, and then has to be analysed before a 'Notice of Intention to Prosecute' is issued. If a digital camera is used instead, or the image from a traditional camera can be converted into digital data, then there are many advantages: incidents can be recorded almost indefinitely as these data are down-loaded to a computer, the data store for many cameras can be at one central and secure location (eg in a police station) rather than by the road, processing is done by computer and, if number plate recognition software is used, the registered owner of the vehicle can be identified immediately. The ultimate in automation is for the computer then to print a Notice of Intention to Prosecute and send it out to the offender without human intervention- although we emphasise that this is not current practice.

1.5 Home Office requirements for digital enforcement systems specify the camera resolution to be used (approximately 1000 x 1500 pixels), image compression standards for when the image is transmitted to the computer, transmission encryption protocols and standards for storing and archiving images. An authentication code is also required to be added to the image. The level of security during transmission of the image data is similar to the encryption used by banks to secure the electronic transmission of data which occurs when a cash machine (automatic teller) is used.

Document imaging

1.6 The Abbey National told us that they had revolutionised their document management system by using optical scanners linked to computers with character recognition software. Original paper versions of mortgage applications, for example, were now scanned electronically to produce a digital image; this was stored in computer memory from which it could be retrieved and viewed at any time. Alterations could not be made to this digital copy, but annotations could be added in the form of overlays to the image (QQ 334-8). The Abbey National told us that the digitisation of documents reduced the risk of loss, damage or alteration, inherent in paper-based processing. The scanning stage was seen as the critical step and this was under secure management; the risk of files being deleted or substituted after this initial processing was controlled through the implementation of an audit trail which recorded all accesses.

Overt surveillance using CCTV

1.7 A surveillance system inside a large shop or a town centre will usually consist of a number of cameras with pan, tilt and zoom controls which feed live colour pictures back to monitors in a control room. The camera output is also recorded and this is usually on to high quality videotape. To extend the period between tape changes, the recordings are often only made at two frames per second. CCTV systems depend to a large extent on the quality of the camera and the lens used. For example a system which might be used in a shopping centre would have a 96x optical and digital zoom, autofocus, 370 degree per second pan and 120 degree per second tilt (to move the camera rapidly between pre-set positions), and an in-built image processing computer.

1.8 Some cameras also have infra red capabilities for surveillance during the hours of darkness, and motion detection sensors to warn operators of unusual activity and start recording more detailed images. For example, the City of London Police use motion detectors to alert operators when a vehicle has transgressed an exit point of the traffic control zone in the City. Other camera features available include: bullet-proof and explosion-proof casings; automatic defence mechanisms, to ensure that if a camera comes under attack it is filmed by its neighbours; systems which automatically switch from full colour to black and white to maximise image resolution if the lighting level drops; and directional microphones.

Covert surveillance using CCTV

1.9 The quality of image available from digital CCTV cameras is still poor compared to the high resolution available with analogue cameras, but one area where they have a great advantage is in covert surveillance. Tiny digital cameras a few centimetres square can now be bought which offer 300,000 pixel resolution and low-light sensitivity. At least one company in the United Kingdom is also offering these cameras disguised in anything from mirrors and pictures to smoke detectors and clocks.

Acknowledgements

1.10 The membership of our Committee is listed in Appendix 1 and the Call for Evidence we issued is set out in Appendix 2. The Enquiry was based on the assistance of a wide range of individuals and organisations who responded to the Call for Evidence: these are listed in Appendix 3. We are most grateful to them all for their time and effort. We also wish to express our thanks to those whom we visited, who made presentations or provided briefing: in particular the City of London Police together with the Symonds Group Ltd; the Greater Manchester Police; the Forensic Science Service, and Epsom and Ewell Borough Council. We have been greatly assisted by our Special Adviser, Mr Chris Reed, of Queen Mary and Westfield College. We very much appreciated the help of all those who have contributed to this Enquiry.