Reversible or lossless data hiding enables host media to be
restored from marked media without any loss of host information.
However, since most of existing lossless data hiding
methods are fragile, hidden data cannot be extracted after
marked media goes through alteration such as JPEG compression.
In this paper, we present a robust (referred to as semifragile)
lossless data hiding method that utilizes sub-sampling
and block gravity center. Gravity center of sub-sampled part
of each block is insensitive to alteration, so it achieves robustness.
This technique can be applied to selective authentication
for images. That is, if a marked image does not change at all,
the hidden data is correctly extracted and at the same time
an original image is recovered. After compression, the hidden
data is still extracted without error. Experimental results
prove that the presented scheme achieves both reversibility
and robustness against the predefined distortion.