Steganography Background Classical steganography Security relies on secrecy of encoding system. Tattoo on a shaved head (440 B.C.), Last word in every sentence, Least-significant bits in an image. Modern Steganography Detectable only if secret information is known. a secret key, etc... Invasive nature leaves detectable traces in medium's characteristic. Secrecy of the information is not degraded, but its hidden nature is revealed, defeating purpose of steganography.