Franken also called on the FBI to limit its use of facial recognition technology. In materials about its pilot program in three states, the agency uses pictures of political rallies as places where the technology could be used, and Franken said he's concerned that law enforcement agencies will use the technology to track people at legal protests and other gatherings.

The FBI has limited its use of facial recognition to criminal cases, said Jerome Pender, deputy assistant director of the information services branch of the FBI's Criminal Justice Information Services Division. The FBI has limited its pilot program to using facial recognition to match faces to a database of known criminals, and the database doesn't contain mug shots of law-abiding people, he said.

The FBI is moving slowly on its use of the technology to identify "grey areas" where privacy concerns may pop up, Pender said. The agency is open to making changes to the program, he said.

Franken also called on the U.S. Federal Trade Commission to require private companies to get permission before identifying a person with facial recognition.

While some witnesses at the hearing raised concerns about facial recognition, others said it's already a useful tool for law enforcement agencies. Facial recognition helps police identify criminals much more quickly than fingerprinting and it can help police and prisons avoid the mistake of releasing the wrong person, said Larry Amerson, sheriff in Calhoun County, Alabama.