[quote name='http://www.dartmouth.edu/~news/releases/2004/07/01.html']Farid and Dartmouth graduate student Alin Popescu have developed a mathematical technique to tell the difference between a "real" image and one that's been fiddled with. Consider a photo of two competing CEOs talking over a document labeled "confidential - merger," or a photo of Saddam Hussein shaking hands with Osama bin Laden. The Dartmouth algorithm, presented recently at the 6th International Workshop on Information Hiding, in Toronto, Canada, can determine if someone has manipulated the photos, like blending two photos into one, or adding or taking away objects or people in an image. [/quote]
Professor believes that his method will eventually be recognized even in a court of law. For some reason I am sceptical about the whole concept. Most probably the reason is that I cannot think of a way you can stretch a pixel

[quote]A digital image is a collection of pixels or dots, and each pixel contains numbers that correspond to a color or brightness value. When marrying two images to make one convincing composite, you have to alter pixels. They have to be stretched, shaded, twisted, and otherwise changed. The end result is, more often than not, a realistic, believable image. [/quote]