An error-free data-hiding scheme for encrypted images

Zhang introduced a novel reversible data-hiding scheme for encrypted images. At the receiver, the hidden data is extracted by exploiting the spatial correlation in the image. But Zhang's scheme does not perform well for smaller block sizes and incurs bit extraction errors during recovery. We eliminate this problem by omitting those blocks from the data-hiding operation that causes extraction errors. To identify those blocks at the receiver, we embed their index information into a small portion of the image using a difference expansion method. The experimental results from the proposed scheme indicate that all the hidden data can be successfully retrieved without errors.