There have also been attempts at hiding data within mp3's as another form of steganography, for example the program MP3Stego does such. Steganography also distorts image files just a bit. The more data to hide in a image the more the distortion and the same goes for smaller and smaller images. If for example the data you wish to hide is a image, its quality will be a bit downgraded when its extracted. I'll leave the rest of the reading up to you