Here is an article that claims that none of those things work: http://www.ettm.com/news/foil_photo_cop.html
It sounds like they are able to enhance the image. I'd be very interested to hear from anyone who has actually used something successfully.
Maybe a device like the Michael Knight had, where he hit a button and his license plate changed, would be a better way to go. Anybody remember the Knight Rider? Perhaps it's still on somewhere outside the US.
I heard a story one time about a guy on a motorcycle in Germany who saw the photo radar at the last minute and reached around behind him and covered his license plate with his hands. They never found out who he was.

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Dean
Santa Barbara, CA
ICQ #300030
1974 280C
1984 300SD