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Eight measurements of the body can identify anyone on earth
Using data from 4,000 U.S. armed services personnel, a forensic anatomist has found that people are more easily and accurately identified by their body measurements than their facial features -- even through clothing.
Teghan Lucas, University of Adelaide PhD student, says that “body recognition,” using just eight measurements, can reduce the chance of finding someone with duplicate measurements to one in a quintillion.
This technique would be useful for criminal and missing persons cases -- and requires less data points than facial recognition to be accurate.
"There's been a lot of work conducted over the years on facial recognition. This makes sense -- humans have evolved to recognize faces, which is part of our survival mechanism, and the face contains some very distinctive features," Lucas says.
Problems arise when the face is covered during a criminal act, or video evidence is of a low quality. The larger measurements of the body are easier to make out and quantify than finer details on the face. Facial expressions can also alter perceptions and measurements of facial features.
Lucas' research was mainly based on measuring the skeletal points of the sample of 4,000 U.S. armed services personnel. An adult's skeleton does not change size during most of their lifetime.
For example, the length of an adult's skeletal structure from their wrist to their elbow will not change for decades -- not until they're of a very advanced age, which makes them unlikely to be the subject of forensic investigations.
"We ran the probability based on the findings from the sample. So what's the probability that you'll find someone with the exact same measurements as you when you've taken eight separate measurements? The probability is one in a quintillion -- 1020 -- which is very comparable to DNA and fingerprints," Lucas said.
Clothing is also no problem for body measurements, as the way gravity acts on it means that the overall shape of the body is still apparent. Any movement -- such as on a security tape -- increases the change of seeing the outline of an individual.
Some measurements -- in most cases circumferential measurements -- are impermanent and not suitable for long-term comparisons. A person might put on weight or muscle that changes the circumference of their calves or forearms, for instance.
The larger measurements provided by the body compared to the face mean that there is more variation between people. For example, in the sample used by Lucas, the length of people's ears varied by only 35mm between the shortest and longest -- whereas the breadth of hips in the sample varied by up to 150mm.
"That's why the body is better -- there are more options with a larger range. The more options you have, the less chance you have of finding somebody with the exact same traits," Lucas added.