This visual cryptography method uses a four sub-pixel subdivision method that I haven't seen before, but almost precisely the same effect is achieved when visually demonstrating a Vernam cipher (a.k.a. one-time pad).<p>1. Create a one-time-pad, or key. This is a set of randomly chosen 1's and 0's. Now, make a bitmap out of this data set, with 1 denoting a white pixel and 0 denoting a black pixel. It will look like static.<p>2. Distribute a copy of the key to the person you are trying to communicate with via a secure channel. (This is the hard part, security wise).<p>3. create your message as a black and white (not greyscale) image. It should have the same dimensions as your key.<p>4. Pixel-wise XOR the key with the message. If the key was well randomized, the resulting cypher will also appear to be perfectly random static.<p>5. Send the cypher to the person who is holding the copy of the key.<p>6. When that person receives the cypher, if he XOR's the cypher with the key, out will pop the original message!<p>The only visual difference to this method vs that in the linked article is that the message won't start to show up when you're a pixel or two out of alignment because there is no four-pixel subdivision. You have to line things up spot-on.<p>The Vernam cipher was originally published in 1926, so it's defintely older than "Visual Cryptography". However, I don't know if the visual demonstrations of it (I've only seen them in lectures, not surprisingly, with transparent overheads!), predate visual cryptography. I've seen a couple of lecturers use this technique to demonstrate how a one-time-pad works and, crucially, why you can't reuse keys more than once.<p>Does anyone know if this Visual Cryptography offers anything useful that a one time pad doesn't? The linked page is very cool and all, and I wish one as well constructed existed for one-time-pads! (Possibly one does, but I was too lazy to spend more than a minute searching for it.)