Who doesn’t love a pretty picture. It seems like everyone is trying to make an already nice picture look even better. I hate to throw a wrench into this fine mechanism, but sometimes an uglier picture is better. Let me rephrase that–sometimes an un-enhanced picture is more desirable. The antithesis of photo enhancement is degrading the photo do draw more meaning. The process of writing and disguising these hidden messages is called steganography. In the case of a photograph, the process is more artistic, but it can also be used for more practical purposes such as watermarking copyrighted images. This is not to be confused with cryptography, which hides the meaning of a message, not the message itself.

This is by no means an new idea. Such a process can be traced as far back as ancient Rome and Greece. These civilizations used stone or wooden tablets covered in wax as a sort of reusable writing slate. So instead of simply writing the message in the wax as was normally done, the message would be inscribed in the stone or wood itself and wax then poured over the message to hide it.

We are now a far cry from stone and chisels, but the point is still valid. You can’t crack a code that you can’t see. This makes it very difficult to decrypt (let alone detect) a message disguised by steganography. To give you an idea: stegoanalysis is the process of detecting steganography, but does not include decryption because it is so hard to accomplish. This fact is rumored to have been put to good use by terrorists.

So, in the cases of watermarking copyrighted material,  tagging notes in online images, or maintaining confidentiality, better is not always better.

http://www.securityfocus.com/infocus/1684

http://en.wikipedia.org/wiki/Stegography