  JPEG is the most popular image format, which is widely used in our daily
life. Therefore, reversible data hiding (RDH) for JPEG images is important.
Most of the RDH schemes for JPEG images will cause significant distortions and
large file size increments in the marked JPEG image. As a special case of RDH,
the lossless data hiding (LDH) technique can keep the visual quality of the
marked images no degradation. In this paper, a novel high capacity LDH scheme
is proposed. In the JPEG bitstream, not all the variable length codes (VLC) are
used to encode image data. By constructing the mapping between the used and
unused VLCs, the secret data can be embedded by replacing the used VLC with the
unused VLC. Different from the previous schemes, our mapping strategy allows
the lengths of unused and used VLCs in a mapping set to be unequal. We present
some basic insights into the construction of the mapping relationship.
Experimental results show that most of the JPEG images using the proposed
scheme obtain smaller file size increments than previous RDH schemes.
Furthermore, the proposed scheme can obtain high embedding capacity while
keeping the marked JPEG image with no distortion.
