Wagner Lipnharski says:
Well, here at Disney, they use to apply a fine white screen (like a curtain) right in front of the scenes they don't want you to photograph, despite they ask not to do, several people just flash their cameras right in middle of a "non-flash-photography-please" show. What happens, is that the flash illuminate the fine screen, and the picture will take only a white curtain, not the scene behind it.I heard that at Universal Studios, they used in the past large infra-red lamps pointing to the public at places where photos were not welcome, so for the film, those lamps just obscure all the scene, but not to the human eye that can't see infra-red.
Using polarized films over the plate could be a solution, since you could arrange two films in a way to block 100% of the light to return to the sender angle. Other light angles would be reflecting more or less normal, so you could read the plate at day light, since the light comes from several different angles. Photo flashes are normally assembled close the the camera, so... hey I am not saying it works, not even pushing you to do it, just telling you what physics can do, some can say that telling the secrets to decode DVD is crime, I would say it is only transfer of knowledge.
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