PHOTOGRAPHS and video footage, usually from CCTV cameras, are becoming routine evidence in court cases dealing with everything from shoplifting to murder. Behind this trend is the notion that 鈥渢he camera never lies鈥�, which we all know to be untrue in this digital age. Although the authenticity of images is rarely questioned in court, it is only a matter of time before a serious miscarriage of justice brings the issue to the fore.
Worryingly, governments and legal institutions have been slow to realise the seriousness of this issue. In the UK, for example, all it takes to have a photo admitted as evidence in a trial is for the photographer to make a statement that it is genuine.
Warnings about the potential for faking digital images are not new. But the proliferation of cheap digital cameras and computers, together with programs for altering photos and editing video footage, is turning that potential into reality. Where once a specialist was needed to alter analogue images, even beginners can now create digital fakes good enough to fool discerning experts.
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In a world where people can be prosecuted for a picture on their computer hard drive, we need to be certain that the image found is real and not a digital creation from somebody鈥檚 imagination. The US has learned this the hard way. Americans who were prosecuted for peddling improper images of young children successfully argued that they had committed no crime because the images were digital fakes. No children had been harmed and the law was eventually changed.
What we need is a reliable way to determine whether an image has been tampered with. Digital watermarking, in which an imperceptible code is implanted within digital media, has proved to be neither practical nor watertight. But the work of people such as Hany Farid of Dartmouth College in New Hampshire is offering new hope (see 鈥淎 picture tells a thousand lies鈥�). Farid has found an ingenious way to check digital images by analysing mathematical properties that are hidden from sight.
Farid鈥檚 work brings us a step closer to ensuring that cameras cannot lie. But it is just a start. More work should be encouraged by governments and legal institutions to improve his techniques or develop alternatives. Courts need guidelines on what digital evidence is admissible and when analysis is needed. Unless action is taken now, photography will lose its special status as a trustworthy record of events: it will become just one more point of contention for lawyers to interpret and reinterpret. That cannot be in the best interests of justice.