A Novel Technique for Image Steganography Using Nonlinear Chaotic Map

Image steganography is the art of hiding information into a cover image. This paper presents a novel technique for Image steganography based on DWT, where DWT is used to transform original image (cover image) from spatial domain to frequency domain. The beauty of steganography technology comes out in more pronounced way when there is no absolute relation between stego and original image and it is possible to rebuild the original image in much easier way. As chaotic systems are known to be more random and non-predictable, they can be made utilized in achieving the encryption. The transposition technology of encryption systems requires scrambleness behaviour in order to achieve the encryption of the data. This srambleness behaviour can be derived from the randomness property of chaos which can be better utilized in the techniques like transposition system. Firstly the henon mapping (chaos) is applied on the secret image and the two dimensional Discrete Wavelet Transform (2-D DWT) is performed on the cover image of size M x N. Then each bit of scrambled image is embedded in the high frequency coefficients resulted from Discrete Wavelet Transform. Image quality is to be improved by preserving the wavelet coefficients in the low frequency subband. The experimental results show that the algorithm has a high capacity and a good invisibility. Furthermore, satisfactory security is maintained since the secret message/image cannot be extracted without knowing initial conditions of the henon map.