The saying "The camera never lies." has been with us almost since the beginning of photography - yet we all now know that it can, and does lie, and very convincingly. Yet most of us still seem to trust the truth of a photographic image - especially in our newspapers or on TV news reports - even though we may question its message. We trust photographs, even if they have been manipulated. Models are Photoshopped to fit ideals of beauty; our own snaps are filtered to add glow and grain. We think of photographs as an accurate reflection of unaltered reality. We're convinced of this when we take unposed snaps on our family holidays or of colleagues the worse for wear at the office party. It is this property of photography that makes it hard to question the evidence before our eyes.

Our holiday snaps, though, like photographs showing life ten, fifty, a hundred years ago, tend only to bring about at most a feeling of nostalgia - not always a negative emotion. Many people keep albums to relive the better moments of their lives - and their impact is reduced by the fact that what they show is over, part of history. News photos, on the other hand, in presenting moments of an event that is probably still going on somewhere, must provoke a more vivid, emotional response.