>From: "dan@geer.org" <dan@geer.org>
   >Here's another one, [1]http://www.nauto.com, which I mention as the
   >recording of license plates and everything else in the surround,
   Nearly 20 years ago, I first heard of "3M Louvered film", thin plastic
   sheets with opaque black plastic molded perpendicularly to the plane of
   the sheet.  It would be very useful to help block the viewing of
   license plates from the side of the road, or above on poles or
   overpasses.  Google-search '3M louvered film".
   [2]http://www.apioptics.com/pdf/3M-Display-Film-Summary.pdf
       [3]http://www.freepatentsonline.com/3919559.html
     [4]http://www.freepatentsonline.com/EP0466460A2.html    Two sheets
   installed perpendicularly to each other would render a license plate
   readable only from a limited viewing cone behind, or in front of, the
   car.

             Jim Bell

References

   1. http://www.nauto.com,/
   2. http://www.apioptics.com/pdf/3M-Display-Film-Summary.pdf
   3. http://www.freepatentsonline.com/3919559.html
   4. http://www.freepatentsonline.com/EP0466460A2.html