Dec 15, 2005

How to Tell If a Digital Image Has Been Altered

Source: CSO
Written By Simson Garfinkel

Digital photography, Photoshop and synthetic computer graphics have made image trickery both easier to commit and harder to detect. But it is still possible to catch tampering—provided you have a good eye and the right tools.

Physical impossibility is a good giveaway. For example, a current advertisement for a four-wheel-drive sedan that shows lots of two-wheel-drive vehicles up on their back wheels (“Why pay for four wheels if you’re only using two of them?”) is clearly faked because the shadows on the pavement don’t match the cars up in the air. So sometimes, detecting a forged image simply requires looking closely. In another recent high-profile example, the crowds in photos released by the Bush reelection campaign in October 2004 had been digitally enhanced with extra faces. Careful observers found that some of the faces were present more than once in the same crowd shot.

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