Steganography is a method of hiding data within an ordinary-looking image or video in order to avoid detection. Files and messages can be embedded into other files in various ways, and then extracted by its recipient. Steganography can be combined with encryption as an extra step for hiding or protecting data.

Links:

What is Steganography?– An article introducing Steganography from Wired magazine.

Digital Invisible Ink Toolkit – A simple Java-based steganography tool that can hide a message inside a 24-bit color image so that knowing how it was embedded, or performing statistical analysis, does not make it any easier to find the concealed information.

Imagemagick – A powerful image creation software that can be used to convert images to and from a variety of formats, including text-based pixel plots. Pre-built into Kali Linux.