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. The most advanced systems allow police to run searches from laptop computers in their patrol cars and offer access to the FBI and other federal authorities.
Such open access has caused a backlash in some of the few states where there has been a public debate. As the databases grow larger and increasingly connected across jurisdictional boundaries, critics warn that authorities are developing what amounts to a national identification system — based on the distinct geography of each human face.