One in a trillion odds of having a real-life doppelganger

November 13, 2015, University of Adelaide

While many people may think they have a doppelgänger (look-alike), new University of Adelaide research has proven the likelihood that two people share the exact same face is in excess of one in a trillion.

University of Adelaide School of Medicine PhD student, Teghan Lucas, used a database containing anthropometric (face and body) measurements of almost 4,000 individuals to search for duplicate . She found that when seven facial metric traits were used (measurements of the head and facial features), she was unable to find any two faces that matched.

Furthermore, through mathematical equations, she discovered that by using a combination of eight facial metric traits, the probability of finding two faces with the same measurements in the general population was less than one in a trillion. The study was published in the journal Forensic Science International.

Ms 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."

"Until now, using facial anthropometric measurements to convict a suspect of a crime didn't stand up in court because there was no proof that no two faces were the same.

"This study has provided overwhelming evidence that facial anthropometric measurements are an effective means for identifying a perpetrator when video or photographic surveillance has captured a crime," she says.

Professor Maciej Henneberg, co-author of the research and head of the University's Biological and Comparative Anatomy Research Unit, says there are two ways to analyse .

"The use of 'descriptive' traits involves adjectives such as 'wide' and 'curved' to categorise such as the nose, while 'metric' traits most commonly involve measuring the distances between specific points on the face," says Professor Henneberg.

"Descriptives are not considered a reliable method of evaluation because a trait such as the colour of someone's eyes is subjective.

"In our study, we solely used metrics (facial anthropometric measurements) of individual's heads, noses, eyes and lips, which were collected by people qualified in anthropometry.

"With what we now know about facial anthropometric measurements, we can measure a suspects' face, compare it to a face captured on video surveillance images and determine if it is the same person," he says.

The research unit is now looking at how they can use mathematics to quickly and accurately collect facial anthropometric measurements from images. They will also use the findings of this study to aid police in forensic investigations.

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8 comments

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BartV
1 / 5 (1) Nov 13, 2015
One in a trillion sounds like awfully high odds. But then they used only eight facial metric traits. I suppose if they make even more complex the odds will go way down.

How fearfully and wonderfully we are made.

supercat765
5 / 5 (3) Nov 13, 2015
so one in a trillion for someone with the same face
but what about with a similar face like just a bit wider
or just a slightly bigger nose
My thought is if you take this from exact values to small ranges the odds would go up and for most people would be similar enough to be "doppelgänger"
Zorcon
1 / 5 (3) Nov 13, 2015
Given a population of 7 billion, one in a trillion means about one person in 140 has one.
dan42day
not rated yet Nov 13, 2015
Cat, I have to agree, if you blow up a digital image of someones face in any photographic software it is very apparent that determining the beginning of a feature within a millimeter is very difficult, even with current HD video standards. Angle measurements are similarly imprecise, adding to the problem of exact measurement. Age and tooth loss will also change measurements involving soft tissue and jaw line. Also, changes in testosterone levels can change even skeletal facial features.

Lex Talonis
2.3 / 5 (3) Nov 14, 2015
Stupid article - and issue.

Seriously.

There is the extremely rare "exact match" (or almost nearly so) and then there are the matches, where very close is close enough.....

Like they happen to look very much like someone else..... who you have not seen for like 10 years and "Hi you look like an old school friend / work place friend / friend of a friend / related too / sister of / brother of"

Like perfect matches are extremely rare, but very close matches, are reasonably frequent.

People who get mistaken for twins, inlaws, siblings, movie stars, etc...
Doug_Huffman
not rated yet Nov 14, 2015
Proof that people are innumerate to extremely large numbers and extremely small numbers.

In infinite cosmological time all possibilities are realized and all their variations. We are unique only in this microcosm. In the infinite megaverse there are many copies of us, but causally isolated.
thefurlong
5 / 5 (5) Nov 14, 2015
Stupid article - and issue.

I don't agree.

There is the extremely rare "exact match" (or almost nearly so) and then there are the matches, where very close is close enough.....

Right, but if you read the article, you would see that the article address this here:
"In our study, we solely used metrics (facial anthropometric measurements) of individual's heads, noses, eyes and lips, which were collected by people qualified in anthropometry.
"With what we now know about facial anthropometric measurements, we can measure a suspects' face, compare it to a face captured on video surveillance images and determine if it is the same person," he says.

The article isn't talking about subjective, approximate, matches. It is talking about exact matches that can be objectively determined by an algorithm and how the low probability of there being an exact match between different people can be used as reliable evidence in a court case.
shoebox22
not rated yet Nov 15, 2015
i think the odds for some one looking the same as another person would have infinite odds as snow flakes from the beginning of time are infinitely different it would apply to people also.

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