This morning, I was reading Lifehacker, like I always do, and I came across this story about hiding an MP3 inside a JPG. The JPG image still works and is viewable, and can be made into a functioning MP3 merely by changing the file extension to (you guessed it) ".mp3." The article references a scenario where one could upload such an "encrypted" music file to Flickr as an image file and share said music with one's friends - legality: dubious. This is cool and all, but it made me think of an interesting project I once did.
*begin recollective dream sequence*
The year is 2005, and I am a young, ambitious, yet-to-be-jaded graduate student. For one of my classes (Computer Architecture), we were given a project where we were asked to embed a secret text message inside a bitmap image without altering the visual appearance of the image. We were also to write a complementary program to extract the hidden message from the bitmap image. We did it - embedded and extracted farily long text messages in an image file without changing the image's visual appearance.
*end recollective dream sequence*
The text hidden in the image was virtually undetectable and could be encoded millions of ways to obscure it even further. I think this is an interesting lesson that data of all types (text in the case, music in the former) could be hidden anywhere, in many types of files. Think about it...