Due to limited resources many states use speed enforcement cameras—also known as photo or video enforcement—to take a digital photograph or video of a vehicle (and its license plate) that violates the speed limit. The use of speed enforcement cameras to issue speeding tickets or citations (mailed to the driver) has been controversial, with claims that it violates Constitutional rights.
Laws vary from state to state and in some states speed enforcement cameras are a permitted enforcement tool; in some states they are prohibited; and in some states they are prohibited unless permitted by a local ordinance (city or town).
To measure the speed of a moving vehicle and issue speeding tickets by photo enforcement, police departments generally use photo or video radar that relies on radio signals and the Doppler Effect or photo and video LIDAR (Light Detection and Ranging) technology that relies on lasers rather than radio waves. These devices require training on their proper use and regular calibration to be accurate.