For example, a sender might start with an innocuous image file and adjust the color of every hundredth pixel to correspond to a letter in the alphabet. Media files are ideal for steganographic transmission because of their large size. In digital steganography, electronic communications may include steganographic coding inside of a transport layer, such as a document file, image file, program, or protocol. Steganography includes the concealment of information within computer files. Whereas cryptography is the practice of protecting the contents of a message alone, steganography is concerned with concealing the fact that a secret message is being sent and its contents. Plainly visible encrypted messages, no matter how unbreakable they are, arouse interest and may in themselves be incriminating in countries in which encryption is illegal. The advantage of steganography over cryptography alone is that the intended secret message does not attract attention to itself as an object of scrutiny. Some implementations of steganography that lack a shared secret are forms of security through obscurity, and key-dependent steganographic schemes adhere to Kerckhoffs's principle. For example, the hidden message may be in invisible ink between the visible lines of a private letter. Generally, the hidden messages appear to be (or to be part of) something else: images, articles, shopping lists, or some other cover text. The first recorded use of the term was in 1499 by Johannes Trithemius in his Steganographia, a treatise on cryptography and steganography, disguised as a book on magic. The word steganography comes from Greek steganographia, which combines the words steganós ( στεγανός), meaning 'covered or concealed', and -graphia ( γραφή) meaning 'writing'. In computing/electronic contexts, a computer file, message, image, or video is concealed within another file, message, image, or video. Steganography ( / ˌ s t ɛ ɡ ə ˈ n ɒ ɡ r ə f i/ ( listen) STEG-ə- NOG-rə-fee) is the practice of representing information within another message or physical object, in such a manner that the presence of the information is not evident to human inspection. The same image viewed by white, blue, green, and red lights reveals different hidden numbers. For the prefix 'Stego-' as used in taxonomy, see List of commonly used taxonomic affixes. For the process of writing in shorthand, see Stenography.

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