The technology available to law enforcement tends to advance at a much faster rate than the laws that check overreach and abuses by police and prosecutors. By the time the courts have addressed how certain technologies fit with the various protections of the Bill of Rights, a new technology is available that creates new concerns. Biometric technology, which enables the identification of individuals based on unique characteristics such as DNA, fingerprints, or even the shapes of people's faces, comes with many concerns for people's Fourth Amendment rights. Facial recognition software (FRS) is now used by both law enforcement and the private sector for a variety of purposes, many of which pose problems not only because of privacy issues, but also because of the risk that the software will make an incorrect identification.
The concern that FRS undermines Fourth Amendment protections against unreasonable searches and seizures is not new, as evidenced by a law journal note published over a decade ago. Nguyen, Alexander T., "Here's Looking at You, Kid: Has Face-Recognition Technology Completely Outflanked the Fourth Amendment?" 7 Va. J. L. & Tech. 2 (2002) (PDF file). Courts have generally held that police may use technology that enhances what individual law enforcement investigators could see on their own, such as cameras used in aerial surveillance, Dow Chemical Co. v. United States, 476 U.S. 227 (1986), or a flashlight used "to illuminate a darkened area," Texas v. Brown, 460 U.S. 730, 740 (1983). The concern, according to the note, arises when technology replaces an investigator's senses rather than merely enhancing them. Nguyen at 12, citing Kyllo v. United States, 533 U.S. 27 (2001).
Most FRS only uses photographs taken in public places, and the general rule for some time has been that people have no reasonable expectation of privacy in public. The Supreme Court has also held, however, that people should be free "from arbitrary surveillance by their government." Nguyen at 18, quoting Dow Chemical, 476 U.S. at 240. The problem with FRS, from that point of view, is that it "subjects everyone, including innocent citizens, to indiscriminate scrutiny." Id. [emphasis in original.]