“Twenty-four hours a day, video from thousands of cameras stationed around Detroit, at gas stations, restaurants, mini-marts, apartment buildings, churches and schools, streams into the Police Department’s downtown headquarters. The surveillance program, which began in 2016, is the opposite of covert. A flashing green light marks each participating location, and the point of the popular initiative, known as Project Green Light, has been for the cameras to be noticed and help deter crime.”