An Adaptive Quad Tree Based Transform Domain Steganography for Textual Data

Abstract

Internet is most popularly used for communication. However, most of these communications are confidential and must not be detected by intruders. Steganography, a well-known traditional approach, provides an efficient way to obscure the presence of such a communication by hiding data in media like images, audio, video, etc. Also, today’s world communicates mostly via images which are known to have very high level of redundancy. As a result, image steganography seems to be the best suitable choice among all the available variants. This manuscript thus presents a block based transform domain image steganography approach to embed a secret text message within a cover image. The approach is designed by combining the concept of quad tree blocks with discrete cosine transform (DCT) which is a transform domain steganography technique. A quad tree decomposition of cover image results in variable sized square blocks. The presented approach adaptively determines locations within variable sized quad tree blocks in a cover image for embedding the secret text. The number of blocks obtained for a cover image is controlled using a threshold and a minimum block size. Results are generated for various combinations of these two values and are analyzed on the basis of capacity, peak signal to noise ratio (PSNR), and structural similarity (SSIM) index. The obtained results prove the effectiveness of the presented scheme over the existing spatial and transform domain techniques (without block and fixed block based) in terms of all the considered parameters. In addition, a visual examination further proves that the presented approach provides good imperceptibility of the secret message, thus hiding the presence of any secret communication.