An interesting <a href="http://www.nytimes.com/2007/10/02/science/02conv.html?_r=3&amp;pagewanted=1&amp;oref=slogin" target="_blank">interview</a> with Hany Farid of Dartmouth College in New Hampshire USA, a specialist in uncovering digital forgeries.

"Not long ago, researchers from South Korea had to retract papers published in <em>Science</em> because the photographs used to prove that human stem cells had been cloned were effectively Photoshop-cloned, and not laboratory-cloned... The Federal Office of Research Integrity has said that in 1990, less than 3 percent of allegations of fraud they investigated involved contested images. By 2001, that number was 26 percent. And last year, it was 44.1 percent.

...when looking at composites of two people, we’ve discovered that one of the hardest things for a forger to match is the lighting. So we’ve developed a way of measuring whether the lighting is consistent within various parts of the image. Lately, I’ve become obsessed with eyes. In a person’s eyes, one sees a slight reflection of the light in the room. So I’ve developed a technique that can take that little image of the reflection of light and tell us where the light was while you were being photographed. Does that match what we see in the image?"

From the  <a href="http://www.nytimes.com/2007/10/02/science/02conv.html?_r=3&amp;pagewanted=1&amp;oref=slogin" target="_blank">New York Times</a> via <a href="http://www.anomalist.com" target="_blank">The Anomalist
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