This just in from the BBC: "The revelation that police are holding a database of around 18 million mugshots has provoked an examination of the balance between civil liberties and catching criminals. But how effective is the technology?
Not as good as many people think, according to the Metropolitan Police officer in charge of the force's central forensic image team.
The system used by the force works by taking measurements between various points on people's faces in order to build up a picture of what they look like.
That is then matched against two databases - one holding mugshots taken of people who have been arrested and the other containing images from outside sources, such as CCTV.
The main problem, Det Ch Insp Mick Neville told the BBC, is that most images are not of a good enough quality to produce any sort of match.
"With the vast majority of CCTV images, it will not work - in 18 months, we have had fewer than 10 hits."
That did not compare well against human performance. Mr Neville said he recently brought 90 "super recognisers" - people who are particularly adept at facial recognition - to Scotland Yard. "We had the best part of 300 IDs over three evenings," he said.
He added that, of the 4,000 images loaded on to the database following the 2011 London riots, only one has actually been matched to a person.
He was speaking after BBC Newsnight reported that many of the people whose images were being held by the police were innocent."
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