Comment by mortov

Static cameras have markings and 2 pictures are taken, normally 1/3 of a second apart. Activation is either radar or in-road inductive wiring. Neither are foolproof and pictures are supposed to be manually checked but often are not with results like this http://www.bbc.co.uk/news/uk-england-norfolk-21264281 where a claimed 50mph was actually 18 mph)