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 key difference between Cryptography and Steganography lies with the fact that when a message is encrypted, one already knows that the message exists and it is encrypted, whereas with Steganography you might not even know (or observe) that there does exists a message too, simply because its hidden behind an image, video or an audio etc… which without keen observation might go without any suspicion. Steganography was also widely used by the terrorists responsible for the 9/11 attacks at the twin towers, this was later figured out during the post attack investigation.
It is fairly easy to hide and then unhide a secret message in a graphic,audio or video file without obviously altering the visible appearance of that file.
Here is one method I came across while learning Steganography. Its comes out of box with our own Dos Commands !
Open Command Prompt (run -> cmd.exe) and type something like this:
copy /B original.jpg + archive.rar new.jpg
If you open new.jpg with some picture viewer it will be a normal image, but when you open it with WinRAR for example it`ll show you the contents of archive.rar.
It will also work with different types of files.
Source : http://blog.rohit.im/hacking-tips-tricks/steganography-dos/