Dynamic Approach of Frequency Based Image Steganography

In this paper, we propose a dynamic approach to image steganography in the frequency domain in order to increase the hiding potential of the cover image. Concealing a secret file in another file for the sake of its safe transmission via the communication channel is the main aim of a steganography technique. Embedding small size messages in a cover image has less possibilities of hampering the quality of the cover image. However, hiding a bigger size file into a cover image is quite challenging as it may distort the cover image quality thereby revealing the existence of the hidden file. Many researchers who have worked in this domain have followed similar steps to process the cover image before embedding the secret message in it. The cover image is first splitted into blocks of 8X8 or 4X4 pixels per bock and the secret message bits are inserted into the cover blocks uniformly. In our work the cover image blocks are converted from the time domain to frequency domain using Discrete Cosine Transformation (DCT). The blocks are further quantized using the standard JPEG (Joint Photographic Expert Group) quantization matrix. The count of secret message bits that are to be hidden in each block is decided based on the number of coefficients remaining in the blocks after quantizing the cover image. Researchers have used Jpeg Quantization Modification Table (JQTM) to increase the capacity of the stego object. One drawback of using modified quantization table is that it might increase the cover file size than any standard JPEG file. Least Significant Bit substitution method is used for embedding purpose. A text file is taken as the secret message in our work. The quality of the stego object is assessed using peak-signalto-noise ratio (PSNR) and mean squared error (MSE).