Cameras installed on high-ways and roads where drivers are expected to drive very fast, allow police to track the cars going over the speed limit by taking photos of their license plates and then matching the image to the number. This way, they end up simply sending you a bill without stopping the traffic and having to keep policemen on the street.
photo courtesy of Chriszwolle
###HOW TO AVOID
install very bright LEDs around your plate, making it impossible to photograph the number;
use photo blocker spray (http://www.motorshop1.co.uk/photoblocker.htm);
install a slave-flash, triggered when you are at risk, overexposing the photograph;