The anti-photo cover is about $60 (radartests.com I believe reviews them), BUT I have heard there is a spray you put directly on the license plate that makes them MORE reflective, this making any photos just become over exposed on the license plate.
This way there is no "cover" over your license plate, which is against the law in some states, and the Anti photo covers are very obvious, and you can get busted for them.
On the other hand, having a MORE reflective license plate means you could possibly get clocked from farther away.
Just some facts, do with them as you will.