By overwriting these pixels with data, and scattering that data throughout the file in a reversible way, you can effectively hide data without increasing the file size or altering the image significantly. In most pictures there are more pixels than can be displayed on the screen.
The first, is hiding data in an image file, within the image itself. There are a few methods of steganography I want to talk about. In a modern sense, steganography is used by cyber criminals to smuggle data out of or into a network passing as regular files. This means trying to hide what you are doing in plain sight.
There is a security principle you will probably hear a lot about, “security through obscurity”. If this sounds a little like cryptography, you are on the right track. In much more recent times, lets say about 500 years ago, steganós and graphia were combined to mean “covered writing”. The paleontologists used the Greek word steganós and sauros to mean “covered lizard”. 150 million years ago, there roamed a dinosaur covered with bony plates. What do dinosaurs have in common with cryptography? Well Greek, apparently, and a lot of time.
