Steganography is the hiding of information in innocent looking objects and is a part of cryptography. Steganos means hidden and graffein write. Since the arrival of digital files for image and sound, steganography has known an enormous revival.

Hiding messages is something that already occurs since ancient times, e.g. Herodotus tells how in the Fifth Century before Christ a sovereign shaves the head of a slave and then had it tattooed. The message contained a warning for Greece about the planned invasion by Persia. When the hair grew back the information was hidden for the outside world and could become visible again by shaving the hair.

An other technique in the old Greece, also described by Herodotus, was writing messages on wood, and then cover them with a coating of wax, so that it looked like an unused bar.

From times immemorial people know ways to write messages on paper with invisible ink.

During the Second World War the Germans and other spies used microdots to send information. These microdots were about as big as the dot written with a typewriter, and they contained nformation made smaller in a photographical way.