A US Senate hearing Wednesday highlighted concern over the growing use of facial recognition technologies, both for law enforcement use and in big social networks like Facebook.

Senator Al Franken, who chaired the judiciary subcommittee hearing, said the expansion of such biometric technologies poses concern over privacy and civil liberties.

Franken said that in law enforcement, the use of facial recognition “will catch criminals,” but “could come at a high cost to our civil liberties” if police use the systems to target “innocent civilians” or political rallies.

He also expressed concern that facial recognition used by Facebook to “tag” or identify members could be abused by divulging information that its members do not want made public.

Representatives of the FBI and Facebook testified about their safeguards, and civil liberties advocates and others offered views on the new technology.

Franken said facial recognition “exists right here today” and that “our federal privacy laws are unprepared to deal with this technology.”