This Demonstration shows a modulo-4 image encryption/decryption scheme based on overlaid hexagonal image elements for paper and film. Drag the key right pane over the left encrypted pane to decrypt the image.
A modulo-4 arithmetic is graphically implemented by overlaying half-opaque/half-transparent hexagons. The 4 possible discrete relative rotations of overlaid hexagonal elements provide 4 "levels of grey". The hexagons tessellate the encrypted and key planes. The correlations between the hexagons in the encryption with the randomly rotated hexagons in the key reveal the image. Of course, for secrecy the key must be secured. Increase resolution for better effect.