Authentication Technique for Gray Images Using DCT (ATGIDCT)

This paper describes a novel steganographic technique based on Discrete Cosine Transform (DCT) for image authentication in frequency domain. The embedding algorithm applies DCT on a sub-image block called mask of size 2 x 2 of spatial components in row major order for the whole carrier image. Single bit of authenticating secret message/image is fabricated only in the real part of the frequency component of 2nd, 3rd and 4th carrier image bytes of each mask. The positions for embedding are pseudorandom in nature owing to a self derived hash function, which helps to improve the robustness of the technique. Also a minor re-adjustment is implemented only on the first component of each mask after embedding to keep the pixel values positive and non fractional in spatial domain. Experimental results prove statistically significantly enhanced performance of the proposed watermark technique.