Shortening the Cover for Fast JPEG Steganography

Recently, the most effective steganographic schemes for JPEG images are based on minimal distortion model with Syndrome-Trellis Codes (STCs) as the coding method. However, the execution time of STCs will be severely long for message embedding to the cover object of large size, which cannot meet the demand for real-time communication in a real-world application. According to the time complexity
$O(2^{h}n)$
, it is suggested in the STCs to accelerate the embedding process by decreasing the constraint height
$h$
. However, smaller
$h$
corresponds to lower steganographic security. In this paper, we investigate the possibility of shortening the cover (reducing the length
$n$
) for speeding up the execution of STCs without weakening the steganographic security. After introducing some properties of cover selection with proofs, we propose several algorithms designed for JPEG images to construct a preferable shortened cover containing DCT coefficients of smaller costs as much as possible. The experimental results display the superiority of the proposed algorithm on the speed profit and the security when compared with the method of decreasing
$h$
. With confidence, a JPEG image of arbitrary quality factor can be safely shortened to 1/4 of the original, and correspondingly the execution of STCs can be four times faster.