Facebook outlines its photo-tagging process in its terms of service and users can opt out of it. The lawsuit will decide whether this measure qualifies as explicit consent under the privacy act.

"The Court accepts as true plaintiffs' allegations that Facebook's face recognition technology involves a scan of face geometry that was done without plaintiffs' consent," U.S. District Judge James Donato wrote in his ruling.

Facebook faced similar privacy concerns in Europe and Canada, and it stopped using the facial-recognition tech in those regions.