Steganography (Part 5, A good video from YouTube)

Steganography (Part 4, Usage and tools)

Steganography can be used for many reasons, some good and some not. Good usage can include things like watermarking images (copyright protection) that they are overlaid in files, which appear to be part of the original file and are thus not easily detectable by the average person. IT also could be used as a way to make a substitute for a one-way hash value. Or it can be used to tag notes to online images (like post-it notes attached to paper files). Finally, Steganography can be used to maintain the confidentiality of valuable information, to protect the data from possible sabotage, theft, or unauthorized viewing.
Unfortunately, Steganography can also be used for illegitimate reasons. For instance, if someone was trying to steal data, they could conceal it in another file or files and send it out in an innocent looking email or file transfer. Furthermore, a person with a hobby of saving pornography, or worse, to their hard drive, may choose to hide the evidence through the use of Steganography. And, as was pointed out in the concern for terroristic purposes, it can be used as a means of covert communication. Of course, this can be both a legitimate and an illegitimate application.

Tools:
There are some tools for implementing the Steganography and in below some of them are available

StegSpy, Steganalysis Stego Suite™, Secret Messages Come in .WAVs, Stegdetect

Steganography (Part 3, Fundamentals)

Steganography just hides the covert message and not the communicating with each parties. The Steganography process generally is putting a hidden message in some transport medium that is called the carrier. The secret message should be embedded in the carrier to form the Steganography medium. A Steganography key may be used for encryption of the hidden message. In summary:

steganography_medium = hidden_message + carrier + steganography_key