A still from surveillance footage, released by the police department in Mesa, Ariz., shows officers surrounding a man after they punched him to the ground.
Mesa Police Department/azfamily/YouTube
High-definition video cameras with 30x magnification keep watch over the Boston Marathon finish line, where two bombs detonated in 2013, killing three people and injuring hundreds.
Micaela Torres and 2-year-old Jakai Johnson swing underneath a surveillance camera at Miwok Park in Elk Grove, Calif. The city's police department collects more than 100 video feeds from across the city.