A category of techniques for secret data communication called steganography hides data in multimedia me-diums. It involves embedding secret data into a cover-medium by means of small perceptible and statistical degradation. In this paper, a new adaptive steganography method based on contourlet transform is presented that provides large embedding capacity. We called the proposed method ContSteg. In contourlet decomposi-tion of an image, edges are represented by the coefficients with large magnitudes. In ContSteg, these coeffi-cients are considered for data embedding because human eyes are less sensitive in edgy and non-smooth re-gions of images. For embedding the secret data, contourlet subbands are divided into 4×4 blocks. Each bit of secret data is hidden by exchanging the value of two coefficients in a block of contourlet coefficients. Ac-cording to the experimental results, the proposed method is capable of providing a larger embedding capacity without causing noticeable distortions of stego-images in comparison with a similar wavelet-based steg-anography approach. The result of examining the proposed method with two of the most powerful steganaly-sis algorithms show that we could successfully embed data in cover-images with the average embedding ca-pacity of 0.05 bits per pixel.
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