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Spotting Faked Photos (Advanced Techniques)

Posted by Matt on June 4th, 2008 filed in Digital Photography Hints & Tips, Photo Manipulation, Photo Workflow

An article in Scientific American describes how experts apply techniques to spot faked photographs. This is mainly for use in Courts to show that images have been faked, but increasingly people are worried that advertising images are so un-real that they can warp young people’s views of their own bodies, causing an increase in serious disorders such as bulimia and anorexia. In courts, faked photos can lead at worse to false imprisonment, so expert opinion is critical.

The techniques described in the article rely on either observed physical effects not matching real world behaviours, or more complex computer algorithms to look for subtler effects. For example under physical effects you can often see a slight mis-match in light sources – both on objects but especially in eye highlights (they should not all be the same, but slightly adjusted based on a person’s position), hallination – a halo effect around objects dropped into one photo from another and excessive smoothness of the face that can look slightly blurry (an effect normally achieved by cloning and overlaying skin from different parts of the face to remove wrinkles). For the more advanced automated scans, repeated blocks of pixels – say from cloning an audience to make an event look more popular – can be detected. At a lower level every digital photo has a ‘fingerprint’ that comes through based on the arrangement of the camera’s CCD, and any adjustments to an image will generally destroy this fingerprint. Sneaky.

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