The first description of the use of steganography dates back to the Greeks. Herodotus tells how a message was passed to the Greeks about Xerses' hostile intentions underneath the wax of a writing tablet, and describes a technique of dotting successive letters in a cover text with a secret ink, due to Aeneas the Tactician.
Pirate legends tell of the practice of tattooing a secret information, such as a map, on the head of someone, so that the hair would conceal it.
Kahn tells of a trick used in China of embedding a code ideogram at a prearranged position in a dispatch; a similar idea led to the grille system used in medieval Europe, where a wooden template would be placed over a seemingly innocuous text, highlighting an embedded secret message.
During WWII the grille method or some variants were used by spies. In the same period, the Germans developed microdot technology, which prints a clear, good quality photograph shrinking it to the size of a dot.
There are rumors that during the 1980's Margareth Thatcher, then Prime Minister in UK, became so irritated about press leaks of cabinet documents, that she had the word processors programmed to encode the identity of the writer in the word spacing, thus being able to trace the disloyal ministers.
During the "Cold War" period, US and USSR wanted to hide their sensors in the enemy's facilities. These devices had to send data to their nations, without being spotted.
Today, steganography is researched both for legal and illegal reasons.
Among the first ones there is war telecommunications, which use spread spectrum or meteor scatter radio in order to conceal both the message and its source.
In the industry market, with the advent of digital communications and storage, one of the most important issues is copyright enforcement, so digital watermarking techniques are being developed to restrict the use of copyrighted data.
Another important use is to embed data about medical images, so that there are no problems with matching patient's records and images.
Among illegal ones is the practice of hiding strongly-encrypted data to avoid controls by cryptography export laws.
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