Speed cameras, computer artwork. Speed cameras are used to photograph vehicles exceeding the local speed limit. As well as a camera, each unit also includes an electronic flash that is used at night. The camera measures a vehicle's speed using either piezoelectric strips embedded in the road, or high frequency radio waves. The photograph taken shows the number plate of the vehicle and has details encoded on the frame (time, date, location and speed). The film is recovered and processed at regular intervals, and notices are issued to drivers. As of 1993, the photograph is admissible as evidence in the case of disputed offences.