HughPickens.com writes: Folk wisdom has it that everyone has a doppelganger; somewhere out there there's a perfect duplicate of you, with your mother's eyes, your father's nose and that annoying mole you've always meant to have removed. Now BBC reports that last year Teghan Lucas set out to test the hypothesis that everyone has a living double. Armed with a public collection of photographs of U.S. military personnel and the help of colleagues from the University of Adelaide, Lucas painstakingly analyzed the faces of nearly four thousand individuals, measuring the distances between key features such as the eyes and ears. Next she calculated the probability that two peoples' faces would match. What she found was good news for the criminal justice system, but likely to disappoint anyone pining for their long-lost double: the chances of sharing just eight dimensions with someone else are less than one in a trillion. Even with 7.4 billion people on the planet, that's only a one in 135 chance that there's a single pair of doppelgangers. Lucas says this study has provided much-needed evidence that facial anthropometric measurements are as accurate as fingerprints and DNA when it comes to identifying a criminal. "The use of video surveillance systems for security purposes is increasing and as a result, there are more and more instances of criminals leaving their 'faces' at a scene of a crime," says Ms Lucas. "At the same time, criminals are getting smarter and are avoiding leaving DNA or fingerprint traces at a crime scene." But that's not the whole story. The study relied on exact measurements; if your doppelganger's ears are 59mm but yours are 60mm, your likeness wouldn't count. "It depends whether we mean 'lookalike to a human' or 'lookalike to facial recognition software,'" says David Aldous. If fine details aren't important, suddenly the possibility of having a lookalike looks a lot more realistic. It depends on the way faces are stored in the brain: more like a map than an image. To ensure that friends and acquaintances can be recognized in any context, the brain employs an area known as the fusiform gyrus to tie all the pieces together. This holistic 'sum of the parts' perception is thought to make recognizing friends a lot more accurate than it would be if their features were assessed in isolation. Using this type of analysis, and judging by the number of celebrity look-alikes out there, unless you have particularly rare features, you may have literally thousands of doppelgangers. "I think most people have somebody who is a facial lookalike unless they have a truly exceptional and unusual face," says Francois Brunelle has photographed more than 200 pairs of doppelgangers for his I'm Not a Look-Alike project. "I think in the digital age which we are entering, at some point we will know because there will be pictures of almost everyone online.