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Published on Aug 2, 2014
Visual cryptography splits a picture into two designs of random-looking black and white rectangles. The original picture appears when decrypted by holding the two parts one on top of the other. A small number of these designs were produced as personalized stamps by the Austrian Post Office, unaware of what they show: the post office had refused to produce stamps with this text some years ago. The method works best if a transparent material is used, but the postage stamps are made of white paper. As seen in the video clip, the original picture is still visible against a strong light behind the two stamps. firstname.lastname@example.org