  This paper presents two novel approaches to increase performance bounds of
image steganography under the criteria of minimizing distortion. First, in
order to efficiently use the images' capacities, we propose using parallel
images in the embedding stage. The result is then used to prove sub-optimality
of the message distribution technique used by all cost based algorithms
including HUGO, S-UNIWARD, and HILL. Second, a new distribution approach is
presented to further improve the security of these algorithms. Experiments show
that this distribution method avoids embedding in smooth regions and thus
achieves a better performance, measured by state-of-the-art steganalysis, when
compared with the current used distribution.
