Often a photograph is used to prove what we say happened, really happened. But digitally doctoring an image has never been easier, and so spotting a fake image is not always as easy as you would think.

However, technology is now catching up with even the most audacious photographic tricksters. Companies have developed software that can tell whether images have been tweaked or tampered with. Photo forensics is a growing field, examining digital fingerprints that can trace images back to the camera or owner.

BBC Click’s David Reid finds out more at an exhibition in Geneva devoted to photo fakery.

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