BPCS-Steganography (Bit-Plane Complexity Segmentation Steganography) is a type of digital steganography. Digital steganography can hide confidential data (i.e., secret files) very securely by embedding them into some media data called "vessel data." The vessel data is also referred to as "carrier, cover, or dummy data". In BPCS-Steganography true color images (i.e., 24-bit color images) are mostly used for vessel data. The embedding operation in practice is to replace the "complex areas" on the bit planes of the vessel image with the confidential data. The most important aspect of BPCS-Steganography is that the embedding capacity is very large.
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The Human visual system has such a special property that a too complicated visual pattern can not be perceived as "shape-informative." For example, on a very flat beach shore every single square-foot area looks the same - it is just a sandy area, no shape is observed. However, if you watch carefully, two same-looking areas are entirely different in their sand particle shapes. BPCS-Steganography makes use of this property. It replaces complex areas on the bit-planes of the vessel image with other complex data patterns (i.e., pieces of secret files). This replacing operation is called "embedding." No one can see any difference between the two vessel images of before and after the embedding operation.
This steganography was proposed jointly by a Japanese researcher and an American researcher in 1997. Their experimental program (titled Qtech Hide & View) is uploaded on an Internet Web site and downloadable for everyone. Recently, many researchers are tackling its algorithm improvement and applications as well as resistibility studies against steganalysis.