Some time ago, I had come across a rather interesting link which had been diffused by a friend of mine concerning how images can be hidden, or indeed, the meaning of said images can be hidden and indeed displayed by the a use of a system called "Visual Cryptography", invented in the early 1990s by two Israeli computer scientists, Moni Na'or and Adi Shamir.
The process works in this manner: You see, it takes two to tango at the best of times and it takes two images to create this image sequence.
Both these images look the same but if you actually drag them over each other than a surprise is in store. This method is a fairly one to try it and it doesn't necessarily have to be done on a computer either
Try this experiment out for yourself, print out both these images on transparent paper, drag one over the other and you'll behold the image at the very top or else you can download both images, run through after effects and/or Flash and drag very gentle over each other and the message should appear like the one on top. 
This method is a fairless flawless method in encrypting data and information, as both images are very necessary in order to create the finalised piece of graphical information. Without one, the other just remains an image that looks like a still from a static afflicted television screen. Links:
A basic page of information in Dutch and English: http://users.telenet.be/d.rijmenants/en/visualcrypto.htm
Try it yourself: http://www.leemon.com/crypto/VisualCrypto.html
