It involves using a Electric Privacy Glass plate over.
Information on the glass: http://www.glass-resource.com/sub/special/privacy.htm
It would be cool to design a system that could somehow detect the presence of a speed camera and then frost the glass covering your plate making the plate completely un-readable. Just need a system that can detect the camera fast enough and also somehow be able to detect non flash cameras. After your car has cleared the camera's view, your glass plate cover becomes clear again. Maybe this "system" could be used in combination with GPS.
The only potential problem I see with it is it takes electric current to keep the glass clear, removal of the current is what makes the glass frost instantly.
I had the idea for some time now. This company I used to work for had a big slab of this glass in the main conference room as a center window. I used to go play with it when no one was around.