And facial recognition—once clunky, slow, and error-prone—can now theoretically turn any police officer’s chest-mounted camera into a sophisticated surveillance apparatus, identifying people as they walk by. California banned the technology in body cameras earlier this year, after civil-liberties groups rallied to stop law enforcement from using facial recognition in cities such as San Francisco and Oakland. The ACLU applauded the law for stopping body cameras from “being transformed into roving surveillance devices that track our faces, voices, and even the unique way we walk.”

Now police-accountability activists are at odds with privacy activists, who worry about an inescapable dragnet that leaves anyone at risk of being scanned, identified, and matched against criminal or immigration databases, all without a warrant or even suspicion of committing a crime.

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“For us, body-worn cameras are an unalloyed, positive good. From the point of view of advocates, it’s a much more complicated situation,” said Jonathan Darche, executive director of the Civilian Complaint Review Board, which investigates misconduct allegations against NYPD officers. “[The cameras] enable us to find out what’s going on with any particular incident far more often than when we don’t have the footage. By having [it], we can make the determination that a … discourtesy was used or an improper threat was used, and that’s been a real game changer for our agency.”

The CCRB’s foremost goal is police accountability. When a person makes an allegation of officer misconduct, the board investigates it by reviewing medical records, acquiring video evidence, and speaking to the complainant, the responding officer, and potential witnesses. Public CCTV cameras can be low-quality and rarely have audio, which is crucial if a person alleges verbal harassment or threats. Bystanders usually record cell-phone video only once they’ve noticed something’s wrong, potentially cutting out useful context. Body cameras, on the other hand, automatically save footage of the 30 seconds prior to the officer pressing “record,” an advance that Darche said has made all the difference in investigations. “We’re able to see what happened before people realized that the incident required recording,” he said.

But some privacy and immigrants-rights advocates argue that sometimes, body cameras bring awareness without bringing justice.

“You take the case around Eric Garner,” said Kesi Foster, an organizer with Make the Road New York, which focuses on immigrants’ rights and police accountability. “Everyone saw what happened in that video,” he said, referring to a viral video of NYPD Officer Daniel Pantaleo putting Garner in a fatal choke hold. “And it still took over five years of organizing and community pressure for one officer … to be held accountable.”