Speed Focus

How traffic speed cameras focus on a plate to make a readable image?

I live and work in China, where the use of cameras now to detect the speed. This is very effective as the police here tend to do nothing, automatic devices are the only way to pick up speed drivers who tend to do badly at any speed. I was told that the plates have a focal point, which I see on my plate. It is built around a dimple a quarter of an inch in diameter and appears to be a different alloy but may be my imagination. It is not painted for some reason, and most are rusty. There is definitely a reason for the dimple and the fact that it is NOT painted. Many people here all the painting over the entire plate to conceal the number of targets of the camera. Not sure if it works, but local police did not seem troubled by the fact that 30% of cars have plates with hidden numbers. Just curious how these focus cameras and what technology is in connection with the dimple in the plate.

<> The cameras are pre-conditions to optimize the image the car. High speed digital cameras make it easy to identify the speeder. No need to focus on a particular object. Sensors in the road trip to camera when a vehicle passes. Here is a description of a particular system: http://www.rta.nsw.gov.au/roadsafety/speedandspeedcameras/fixeddigitalspeedcameras/howdofixeddigitalspeedcameraswork.html

Speed Focus

Speed Focus