| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for preventing image pickup which doesn't use infrared rays. SOLUTION: The method radiates disturbing visible rays of which the optical image is hardly discriminated from an image projected on a screen due to visual characteristics of human beings and is recorded distinguishably from the image on the screen due to image pickup characteristics of an image pickup means in the case of wrong image pickup of the image on the screen.
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