  We show that the quantum nature of light can be used to hide a secret message
within a photograph. Using this physical principle we achieve
information-theoretic secure steganography, which had remained elusive until
now. The protocol is such that the digital picture in which the secret message
is embedded is perfectly undistinguishable from an ordinary photograph. This
implies that, on a fundamental level, it is impossible to discriminate a
private communication from an exchange of photographs.

Quantum Physics;Cryptography and Security