An improved VLC-based lossless data hiding scheme for JPEG images

In this paper, a lossless data hiding scheme which directly embeds data into the bitstream of JPEG images is presented. For real cases, the JPEG code space is partly occupied, not all variable length codes (VLC) in the Huffman table are used during the JPEG image compression process. Thus, these unused VLCs can be made used of and data hiding can be performed by mapping one or more unused VLCs to one used VLC. Through analyzing the statistics of both used and unused VLCs, the proposed scheme can take full advantage of the unused VLCs by mapping Huffman codes according to a specific mapping strategy and reach higher capacity. The output stego image can keep exactly the same content as the original one and preserve the same file size, and if the file size is allowed to be enlarged, then our scheme can achieve a significant improvement of embedding capacity. (c) 2013 Elsevier Inc. All rights reserved.