Clay models look like faces 'by chance'
Clay reconstructions of faces used to identify corpses only look like the real person by chance, according to a controversial report by an Australian anatomical scientist.
Dr Carl Stephan from the University of Adelaide said these facial reconstruction methods, which are also used to build a fuller picture of archaeological remains, are inaccurate and unscientific.
He published his report in the journal Science & Justice.
Soft tissue reconstruction uses clay to estimate how a person looked based on average characteristics of the face and skull. Scientists assume there are standard facial relationships, such as the ratio of the width between the eyes and the width of the mouth.
Scientists also look at the average depth of the skin on the face by sticking pins in corpses. They use this information to build a set of guidelines to pinpoint where a person's eyebrow or nose should be. An artist then models the face in clay.
These techniques are "full of errors", Stephan told ABC Science Online, and the methods used to reconstruct a face are not science but "mostly art".
"I don't think its possible to create a recognisable face," said Stephan, who reconstructs faces himself.
He said that his own facial reconstructions could only approximate a person's face "by chance".
Small errors such as the position of the corner of the eyes, the projection of the nose and the height of the eyebrow accumulate until the actual face is very far away from the person you are trying to identify, Stephan said.
Comparing data published on cadavers' facial characteristics showed that the guidelines used in facial reconstruction "don't match up", Stephan said.
The scientifically verified guidelines used for facial reconstruction, such as the average tissue depth of facial skin, come from data taken from small studies, Stephan said, and do not represent most of the population.
"Hardly anyone has exactly average depth; it's more individual," he said.
It is difficult to determine a person's racial origin or even their sex based on their face, despite what many people think, according to Stephan.
Computing and software engineering researcher Professor Robyn Owens, from the University of Western Australia, said modern techniques of facial reconstruction, using magnetic resonance imaging (MRI) and computers, are more accurate than traditional methods.
But Owens said that basically facial reconstruction techniques work.
"In forensics, facial reconstruction is used to help identify an unknown victim so at the worst it doesn't help, at the best it identifies who the victim might be and other evidence can verify this. It's important because it can also identify who the victim definitely isn't."
Owens agreed that the small data sets used for facial reconstruction weren't reliable and said that more information based on MRI was needed.
"Currently they stick pins in corpses to see how far the skin goes. This is problematic because the skin may have changed after death. Also the data is scarce as it's only taken from a few points in the skull," Owens told ABC Science Online.
She also said the technique can be used to differentiate between the sexes but agrees that racial origin can be tricky.
"Anthropologically there are guidelines that say the groups with different racial origins have different faces, but nowadays they are not so separate. You can tell male and female and you can get an idea of age, and you might be able to pick racial origin," she said.