Police body cameras are seen on a mannequin at an exhibit booth by manufacturer Wolfcom at the International Association of Chiefs of Police conference in Chicago, on Oct. 26. Jim Young/Reuters/Landov hide caption

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Taser International is now selling police departments the technology to store videos from body cameras. Patrick T. Fallon/Bloomberg via Getty Images hide caption

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Oakland police officers, wearing body cameras, form a line during demonstrations against recent incidents of alleged police brutality nationwide. Elijah Nouvelage/Getty Images hide caption

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Cellphones were used to record a 2012 confrontation between protesters and police in Springfield, Ill. Seth Perlman/AP hide caption

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Body cameras, like this one shown at a 2014 press conference in Washington, D.C., are small enough to be clipped to an officer's chest. Washington and Denver are among U.S. cities trying the cameras. BRENDAN SMIALOWSKI/AFP/Getty Images hide caption

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A Philadelphia police officer demonstrates a body-worn camera being used as part of a pilot project last December. Matt Rourke/AP hide caption

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Few police departments have required officers to wear body cameras, but that's changing after the events in Ferguson, Mo., this summer. Jim Mone/AP hide caption

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Evesham, N.J., is one of thousands of U.S. police departments that use body-worn cameras. Joe Warner/South Jersey Times/Landov hide caption

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