Originally Posted by quantum-x

Yes.
It's called steganography - and it's been around for literally hundreds of years.
Essentially, it's the science / art of concealing something in another.

Dating back hundreds of years ago with artists putting paintings inside, behind, and in paintings [...davinci code anyone] - modern implementations include hiding text within text and datafiles [IE, on fat 32, a cluster is 32kb. When you save a file smaller than 32kb, an entire cluster is taken, but the remainder is empty - and this can be used to store 'hidden' data], or the classic of storing something within an image.

For example-

Grab a copy of:
http://users.telenet.be/d.rijmenants/en/steganote.htm

Download
http://ninjito.com/dump/qx-transit-3.bmp

Use the password 'gofuckyourself' - and preseto.

Data within data.

There are many implementations of similar software - files in images just happens to be the most impressive / dramatic.

http://en.wikipedia.org/wiki/Steganography might prove interesting.