  In the paper "Robust reversible data hiding scheme based on two-layer
embedding strategy" published in INS recently, Kumar et al. proposed a robust
reversible data hiding (RRDH) scheme based on two-layer embedding. Secret data
was embedded into the most significant bit (MSB) planes to increase robustness,
and a sorting strategy based on local complexity was adopted to reduce
distortion. However, Kumar et al.'s reversible data hiding (RDH) scheme is not
as robust against joint photographic experts group (JPEG) compression as stated
and can not be called RRDH. This comment first gives a brief description of
their RDH scheme, then analyses their scheme's robustness from the perspective
of JPEG compression principles. JPEG compression will change pixel values,
thereby destroying auxiliary information and pixel value ordering required to
extract secret data correctly, making their scheme not robust. Next, the
changes in both bit plane and pixel value ordering after JPEG compression are
shown and analysed by different robustness-testing experiments. Finally, some
suggestions are given to improve the robustness.
