The embedding operation in practice is to replace the "complex areas" on the bit planes of the vessel image with the confidential data.
In this case the data is passed through a binary image conjugation transformation, in order to create a reciprocal complex representation.
This form of steganography was proposed jointly by Eiji Kawaguchi and Richard O. Eason in 1998.
[1] Their experimental program (titled Qtech Hide & View) is freely available for educational purposes.
[2] Recently, many researchers are tackling its algorithm improvement and applications as well as resistibility studies against steganalysis.