Our streets bristle with CCTV cameras but tracking suspects requires long trawls through hours of footage. Facial recognition software is one shortcut, as is a new system that tracks clothing logos. How does it work?
Commit a crime and chances are you'll be caught on camera during, before or after, for the UK spends more on CCTV than any other European country.
But often the perpetrator's face is obscured, by a hooded top, a bandana or simply the camera angle. So using this footage to solve crimes is difficult, and among police proposals to improve conviction rates is to try new software that will automatically search footage for distinctive clothing worn by unidentified offenders.
It's technology currently used by the sponsors of sporting events to track the visibility of their logos during TV coverage. Its developers say the search will work for anything "lost" - a missing person, a bomb-laden car or a suspect in a logo jacket.
When suspect on CCTV has face obscured, police feed a still of any distinctive clothing into system
It analyses this image, such as a logo, and scans other footage and police databases for matches
Once the item to search for is selected - a Nike T-shirt worn during a shop robbery, for instance - the computer analyses it, pixel by pixel.
It then scans for matches in the police database and footage from other CCTV cameras in the area, and provides a list of search results to help identify and locate the suspect.
"We say to the machine, 'there's a Coke logo, go and find it'," says David McIntosh, of Omniperception. "The technology is like a bloodhound. You give it a smell and it will go off looking for it."
For example a camera might only have a clear of shot this fictional Nike-clad suspect from 150 yards away. Feed this image into the system, and it will recognise the outfit filmed from other angles and distances, even if partially obscured.
The best results are gleaned from giving the computer an image of a suspect, rather than feeding it "clean" brand logos.
David McIntosh explains how the technology would work in searching for missing people, on BBC1's Missing Live
The value to police is that many young criminals wear tracksuits and jackets with distinctive logos, while obscuring their faces with hoods and hats. And they often wear these street 'uniforms' repeatedly as they commit different crimes.
The first police pilot is likely to be carried out by the new Visual Images, Identifications and Detections Office (Viido), which aims to improve the way CCTV footage is processed.
Detective Chief Inspector Mick Neville, of the new London-based unit, has said that despite investing so heavily in surveillance cameras, it takes an enormous amount of police time to scan footage themselves.
"We have these very expensive cameras solemnly starting up and down our streets, but where are the brains behind the eyes?" says Mr McIntosh.
He says the system could help track a suspect's movement before and after an offence. This may throw up footage of their face without hat or hood, or even where they live.
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He estimates it has taken 500 man years to develop the technology in conjunction with the University of Surrey's Centre for Vision, Speech and Signal Processing.
To use the technology police forces would buy a "black box" - essentially a computer - to plug into their video surveillance units.
The kit is already sold to sports marketing companies to measure a brand's exposure on TV.
This system - called Magellan - automatically tells firms how many times their logo appeared during coverage of a particular event, its size, prominence and the length of time on screen.
"Previously there would have been people to do that, but it took five hours to analyse a 90-minute football game," says Mr McIntosh.
Each unit costs about £100,000, with an additional fee for the marketing firms cover maintenance and support services.
DCI Neville has said he wants criminals to "fear" CCTV more, but the challenge for the police is getting the systems - and the budgets - in place to make the most of the images caught on camera.
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