On the Importance of the DCT Phase for Image Steganography Schemes

There is a well-known theory in the literature that as long as the Fourier phase of an image is maintained intact, the overall appearance of an image remains specious if the Fourier magnitude of the image is slightly modified. However, the Discrete Cosine Transform (DCT) is the real number transformation version of the Fourier transform. Therefore, there is no phase spectrum in the DCT transform. However, it is noticeable that several state-of-the-art DCT hiding schemes treat the DCT signs as phase signals, and hide only in the DCT magnitude spectrum. However, there is no solid study on the importance of the DCT signs (phase) on image steganography schemes. Thus, this paper aims to highlight the impact of the DCT phase on hiding schemes, and to discover the degree of improvement achieved by simply keeping the DCT signs intact while hiding the secret message.