EDIT:The technique used to hide the specifications inside image files is a high-tech version of a process called steganography, which has been around since the beginning of recorded history. During the Roman Empire secret information was tattooed on a messenger's shaved head. When the hair grew back, the messenger was sent out with the secret message on his scalp and a decoy message in hand.

In the IT realm, steganography replaces unneeded bits in image and sound files with secret data. Instead of protecting data the way encryption does, steganography hides the very existence of the data. And it's undetectable under traditional traffic-pattern analysis.

There are few legitimate uses for steganography, say forensics professionals. And despite reports circulating about terrorists using steganography to communicate secretly, experts doubt that's the case. Source: http://www.computerworld.com/article/2576708/security0/steganography--hidden-data.html