Attack LSB Matching Steganography by Counting Alteration Rate of the Number of Neighbourhood Gray Levels

In this paper, we propose a new method for attacking the LSB (least significant bit) matching based steganography. Different from the LSB substitution, the least two or more significant bit-planes of the cover image would be changed during the embedding in LSB matching steganography and thus the pairs of values do not exist in stego image. In our proposed method, we get an image by combining the least two significant bit-planes and divide it into 3x3 overlapped subimages. The subimages are grouped into four types, i.e. T ₁,T ₂, T ₃ and T ₄ according to the count of gray levels. Via embedding a random sequence by LSB matching and then computing the alteration rate of the number of elements in T ₁, we find that normally the alteration rate is higher in cover image than in the corresponding stego image. This new finding is used as the discrimination rule in our method. Experimental results demonstrate that the proposed algorithm is efficient to detect the LSB matching stegonagraphy on uncompressed gray scale images.