The Metropolitan Police have called on Londoners to report sightings of suspects in the London riots last year, using the force's Facewatch iPhone app.

Facewatch, which was launched in April, is a free app. Users enter their postcode and will then be shown a series of CCTV images of suspects who the police wish to speak to.

"My hope is that the two-thirds of Londoners who own smartphones will download this app, and help us identify those suspects we still need to speak to," said Mark Rowley, Metropolitan Police assistant commissioner and head of specialist crime and operations.

"We need Londoners to browse through the app every week or so as new images will appear regularly. This is a fantastic way for Londoners to help us to fight crime."

Facewatch

Rowley assured reporters that civil liberties were properly considered when designing the app.

"The police have always used images in public appeals," he said. "So there's no change there. This is using technology to bring those appeals to a much bigger audience.

"Everyone has concerns about a possible infringement of civil liberties but most people also want to see criminals caught. We talked to [human rights groups including Big Brother Watch and Liberty] and they did not have any concerns that those rights were breached by this Facewatch app."

It seems like a decent idea, although some question marks have been raised over the execution: the Facewatch app has picked up more than its fair share of 1-star reviews. It's free, so download it and see for yourself.