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In frequency domain steganography, use of gray scale images for secret data hiding has already been proved authentic. But to enhance the level of authenticity and secrecy of steganography and also to increase the volume of data to be hidden, pairs of gray scale carrier images are used in the proposed work. Each image is considered as a collection of contiguous blocks. The spatial values in each block of size 2 x 2 are first converted to frequency components by applying Discrete Cosine Transform (DCT). Then a message digest is generated for the payload/secret data. Both the payload data and the generated message digest are fabricated within the carrier frequency components. The first frequency component of each block is not used for embedding but is used for re-adjustments to maintain the quantum values positive and non-fractional in spatial domain and also to reduce the integrated noise due to embedding of payload. Further, to enhance the strength of secrecy of the embedded message a method has been devised which deduces pseudo-random positions for embedding and subsequent extraction of secret data bits. Finally, each block of frequency components is reverted back into spatial domain by applying Inverse Discrete Cosine Transform (IDCT). The results, after experimenting with the proposed technique, establish its superiority over other similar techniques in terms of capacity and imperceptibility.
Keywords: Image Authentication, Digital Watermarking, Steganography, DCT, IDCT, MSE, PSNR, IF, SSIM
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