A high-capacity coverless image steganography method based on double-level index and block matching

Recently, a new information hiding technology called coverless information steganography (CIS) is proposed, which uses the original natural image as stego image for the transmission of secret information which can resist the detection of image steganalysis algorithm, so it received extensive attention and support. However, it is still a low hidden capacity of the CIS methods up to now. This paper proposes a high-capacity coverless information steganography technology. In which we divide the cover image into several image blocks and every image block can represent one bit secret information which improves the capacity greatly. Then we retrieve the image blocks for replacement from the image block database based on secret information and then synthesize them into stego image. The quality of the stego image is still high because the required image blocks are similar to cover image blocks and they are all from natural images. Moreover, in order to improve the retrieval efficiency, we have established a double-level index structure. The experimental results show that compared with the existing CIS methods, the proposed method has larger capacity and better visual quality.