Monday, October 01, 2007

Digital forensics

At the Times, Claudia Dreifus interviews Hany Farid of the Image Science Laboratory at Dartmouth:
I think like a forger. I spend a lot of time in Photoshop making digital forgeries to learn the tools and techniques a forger uses. We’ll make a composite photograph of two people and ask, “How do you manipulate this photograph to make it compelling?” By working backwards, we learn the forger’s techniques and how to detect them.

For instance, 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?
And a funny final exchange:
Q. What’s been the most interesting use of your software?

A. I sold a copy of it to a Canadian company that runs a bounty fishing contest. People send in photographs of fish they’ve caught. My program can check if the fish in the picture has been enlarged. We can prove whether or not the fish was really “THIS big!”


  1. In Blade Runner Deckard tracks Zhora from a relection in an eye in a photograph.

    Life imitates art, eh?

  2. Yes! I expect the Blade Runner scene is partly why it caught my eye...