The faces of more than 120 million people are in searchable photo databases that state officials assembled to prevent driver's-license fraud but that increasingly are used by police to identify suspects, accomplices and even innocent bystanders in a wide range of criminal investigations. The facial databases have grown rapidly in recent years and generally operate with few legal safeguards beyond the requirement that searches are conducted for law enforcement purposes." The most widely used systems were honed on the battlefields of Afghanistan and Iraq as soldiers sought to identify insurgents. The increasingly widespread deployment of the technology in the United States has helped police [identify people who] leave behind images on surveillance videos or social-media sites that can be compared against official photo databases. But law enforcement use of such facial searches is blurring the traditional boundaries between criminal and non-criminal databases, putting images of people never arrested in what amount to perpetual digital lineups. Though not yet as reliable as fingerprints, these technologies can help determine identity through individual variations in irises, skin textures, vein patterns, palm prints and a person's gait while walking. Facial-recognition systems ... can be deployed remotely, without subjects knowing that their faces have been captured.