Steganography is a method of hiding data inside an image or a sound file using the imprecision which that image is stored. In jpg photos, the quality can be dialed down quite a way before the changes become noticeable.
Various techniques are used for hiding data such as
- Hiding messages in the lowest bits of noisy images or sound files.
- Hiding data in encrypted data or in random data. The data is first encrypted before being used to overwrite part of a much larger block of encrypted data or a block of random data.
- Mimic functions convert a file to have the statistical profile of another to stop statistical methods that help brute-force attacks.
- Hide messages in modified executable files, using redundancy in the i386 instruction set.
- Embed pictures in video material.