Steganography with Multiple JPEG Images of the Same Scene

It is widely recognized that incorporating side-information at the sender can significantly improve steganographic security in practice. Currently, most side-informed schemes utilize a high-quality "precover" image that is subsequently processed and then jointly quantized and embedded with a secret. In this paper, we investigate an alternative form of side-information - a set of multiple JPEG images of the same scene - for applications when the sender does not have access to a precover. The additional JPEG images are used to determine the preferred polarity of embedding changes to modulate the costs of changing individual DCT coefficients in an existing embedding scheme. Tests on real images with synthesized acquisition noise and on real multiple acquisitions obtained with a tripod-mounted and hand-held digital camera show a rather significant improvement in empirical security with respect to steganography utilizing a single JPEG image. The proposed empirically determined modulation of embedding costs is justified using Monte-Carlo simulations by showing that qualitatively the same modulation minimizes the Bhattacharyya distance between a quantized generalized Gaussian model of cover and stego DCT coefficients corrupted by AWG acquisition noise.