John Menick

From the BBC:

Japanese firm Fujitsu is pushing a technology that can encode data into a picture that is invisible to the human eye but can be decoded by a mobile phone with a camera….The technique stems from a 2,500-year-old practice called steganography, which saw the Greeks sending warnings of attacks on wooden tablets and then covering them in wax and tattooing messages on shaved heads that were then covered by the regrowth of hair.