Progressive quality degradation in JPEG compressed image using DC block orientation with rewritable data embedding functionality

This paper proposes a novel block rotational method to degrade quality and embed external data in JPEG compressed image. The orientation of each non-overlapping DC coefficients block is exploited to embed information while introducing distortion. To achieve progressive quality degradation, size of DC coefficients block is manipulated and the proposed embedding process is applied recursively by shrinking block size in each iteration. Markers are added into the blocks as pre-processing steps to ensure that the original orientation always yields the smallest difference. A post-processing is also proposed to erase the marker introduced for recovering image at higher quality, making the proposed method a rewritable method but not complete reversible. Experiments are conducted to verify the basic performance of the proposed method and comparisons with the conventional methods are also carried out.