This sounds like a great product... wonder if it's legal though:

PhotoBlocker is a special reflective spray that’s supposed to be able to make it impossible for traffic cameras to capture an image of your car’s license plate when you’re speeding or running red lights.

Oh, they have an answer!

Q. Is this product legal?

A. YES. The law in most countries requires your license to be legible to the naked eye. PhotoBlocker Spray is a high gloss, clear, reflective spray that is undetectable. It causes no distortion nor does it obstruct your license plate’s view. YOUR LICENSE PLATE WILL BE VISIBLE TO THE NAKED EYE. Besides, no one will even know you have it on. It only fools the cameras.

Cool.

Link from Autoblog, original article from Engadget.