Reversible data hiding in encrypted images based on overlapping block partitioning and shared-MSB encoding

Reversible data hiding in encrypted images (RDHEI) allows secret data to be embedded into an encrypted image while enabling lossless recovery of the original image. Its practical payload, however, remains limited by the embedding room available in the encrypted domain. This paper proposes an RDHEI method based on overlapping sub-block partitioning and shared-MSB encoding to improve the net embedding capacity. Each encrypted image block is organized into four overlapping sub-blocks. A boundary pixel shared by two adjacent sub-blocks serves as the reference pixel of the next sub-block, thereby increasing pixel reuse. The shared most significant bits within each sub-block are then exploited to create embedding room. Experiments on six standard images show an average net embedding capacity of 408,730 bits, representing improvements of 5.61% and 17.88% compared with two existing methods. Additional experiments on 100 randomly selected images from each of the BOWS-2 and BOSSBase datasets also show higher average net embedding capacities. Moreover, the proposed method provides error-free data extraction, exact image recovery, and separable operation according to the available keys.