[side topic] The last-linked "additional information" mentions rotated 1/2-circles with black & white halves to define greyscale images. There's an easier way, and it'll scale to as many layers and colors as you want: pixel(r,g,b) = ((r1^r2), (g1^g2), (b1^b2)). (bit-level xoring) More layers just add in their values. Until you add all of them, there's no way to know what the final value for a pixel will be. As for th…
You can avoid the waste of space implied by the circles by using ½×1 rectangles instead: http://lists.canonical.org/pipermail/kragen-hacks/2007-March... The interesting thing about the original technique (to me) is that you can do the decryption without a computer. If you want to do this in color, I think you need to use the LCD approach of having red, green, and blue subpixels next to each other.
Re: Visual Cryptography
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