Facebook must face a class action lawsuit over its use of facial recognition technology, a California judge has ruled.A lawsuit in Illinois alleges that Facebook gathered biometric information without users' explicit consent.It involves the “tag suggestions” technology, which spots users' friends in uploaded photos. The lawsuit says this breaches Illinois state law.In an order this week, US District Judge James Donato ruled to certify a class of Facebook users – a key legal hurdle for a class action suit.In a successful class action suit, any person in that group could be entitled to compensation.The class of people in question is made up of Facebook users “in Illinois for whom Facebook created and stored a face template after 7 June 2011,” according to the court order.In Judge Donato's ruling, he laid out the four-step process behind the technology:Initially, the software tries to detect any faces in an uploaded photo It standardises and aligns them for size and direction Then, for each face, Facebook computes a face signature – a mathematical representation of the face in that photoFace signatures are then run through a stored database of user face templates to look for similar matches.The tag suggestions feature is not currently available in the UK.On its help pages, Facebook says the face templates are made from information about the similarities in every photo the user has been tagged in.”If you've never been tagged in a photo on Facebook or have untagged yourself in all photos of you on Facebook, then we do not have this summary information for you,” the company says.The feature is not available to users in most countries, including the UK – and can be turned off in settings for US users.

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