US Patent 7313248 Steganographic image encoding

A steganographic image encoding method (100) is disclosed. The method (100) defines a candidate set of incoherent pixel groups in a digital image, each pixel group comprising at least two pixels. A subset of the candidate set of pixel groups is selected using a predefined selection criterion and an integer colour value is assigned to each of a plurality of colours. The information is embedded in the image by modifying colour values of pixels of the selected subset of pixel groups such that the information is embedded in accordance with the order of the integer colour values corresponding to the colour values after modification.