Steganography | Stegnography
Steganography is the art and science of hiding messages. Steganography is often combined with cryptography so that even if the message is discovered it cannot be read.
The word stegnography is derived from the Greek words "steganos" and "graphein", which mean "covered" and "writing." Steganography, therefore, is covered writing.
Historical stenganography involved techniques such as disappearing ink or microdots. Modern stegnography involves hiding data in computer files.
It is fairly easy to hide a secret message in a graphic file without obviously altering the visible appearance of that file.
Steganography is not encryption. The point isn't to make the information impossible to decrypt, but rather to hide the data in the middle of innocuous data. Usually, this is done by modifying the image pixels in some way, e.g., by slightly modifying the color of the pixels.