Some speed camera vans flash and others do not. Mobile cameras do not usually flash while some statics ones do. This is dependent on the brand of the camera.
There are different speed cameras in the market, and they are used by police officers and other authorities to catch motorists who are over speeding. The cameras are rear facing, and they are able to differentiate vehicles and their set speed limits. Speed cameras are rear faced in order to prevent accidents since they can distract motorists when they flash. They all take pictures of the vehicle. Those that do not flash usually have infrared flash.