Originally posted by BuzzLY
You said you were going to give us a clue. Maybe it's time for one?
http://en.wikipedia.org/wiki/Steganography
The larger the cover message is (in data content terms -- number of bits) relative to the hidden message, the easier it is to hide the latter. For this reason, digital pictures (which contain large amounts of data) are used to hide messages on the Internet and on other communication media. It is not clear how commonly this is actually done. For example: a 24 bit bitmap will have 8 bits representing each of the three colour values (red, green, and blue) at each pixel. If we consider just the blue there will be 28 different values of blue. The difference between say 11111111 and 11111110 in the value for blue intensity is likely to be undetectable by the human eye. Therefore, the least significant bit can be used (more or less undetectably) for something else other than colour information. If we do it with the green and the red as well we can get one letter of ASCII text per 3 pixels.