The word steganography comes from two greek words steganos, meaning "covered or protected", and graphei, meaning "writing". The use of the term was first recorded in 1499 by Johannes Trithemius in his Steganographia, a treatise on cryptography and steganography, disguised as a book on magic.
Generally, the hidden messages will appear to be (or be part of) something else: images, articles, shopping lists, or some other cover text. For example, the hidden message may be in invisible ink between the visible lines of a private letter.
We can say then that steganography is the technique used for hiding a secret message within an ordinary message so that we can extract it at the destination to maintain confidentiality of data.
The purpose of this exercise is to show you some images in their original format, then hide some other files or other images in them. We can then compare the two to see if we can spot any differences.