JUST DAYS AFTER SARAH PALIN’S SELECTION last August as the Republican vice presidential candidate, a photo of a bikini-clad, gun-toting Palin blitzed across the Internet. Almost as quickly, it was revealed as a hoax— a crude bit of Photoshop manipulation created by splicing an image of the Alaska governor’s head onto someone else’s body. From start to inish, the doctoring probably took no more than 15 minutes. Altering digital imagery is now ubiquitous. People have come to expect it in the fashion and entertainment world, where airbrushing blemishes and wrinkles away is routine. And anyone suring the Web is routinely subjected to crude photographic mashups like the Palin hoax, whose creators clearly aren’t interested in realism but in whatever titillation or outrage they can generate. But other photo manipulations demonstrate just how diicult it has become to tell altered images from the real thing. For example, in 2005 Hwang Woo-Suk, a South Korean professor, published a paper in one by HANY FARID 42 INT • IEEE SPECTRUM • AUGUST 2009 WWW.SPECTRUM.IEEE.ORG Doctoring digital photos is easy. Detecting it can be hard SEEING IS NOT BELIEVING