Multilayer reversible data hiding via histogram shifting

Concealing messages from unauthorised people has been desired since written communication first began. With advancements in digital communication technology and the growth of computer power and storage, the difficulty of ensuring the privacy of individuals and the protection of copyright has become increasingly challenging. Steganography finds a role in attempting to address these growing concerns. Problems arise in the steganography method because of the trade-off between capacity and imperceptibility whereby increasing the embedding capacity increases the distortion in the stego object and it thus becomes suspect. Another problem is concerned with non-retrieval of the original cover object whereby misplacing data could be crucial for example in the case of medical images. Reversible data hiding technique based on histogram shifting addresses the problem of retrieving the original cover. Embedding the secret message by shifting the histogram between the pair of the peak and minimum points wastes the embedding capacity and does not control the distortion in the stego image for various secret messages sizes. In this research, a technique for reversible data hiding is proposed which enables the retrieval of both the hidden secret message and the original image at the receiver’s side. The proposed technique considers the size of the secret message and the distribution of the colour values within the cover image to determine the value of the optimal pair or set of container and carried colours within the best sub image instead of the pair of peak and minimum points. The experimental results show that the proposed technique increases the embedding capacity within the cover image and produces a stego image with a high peak signal-to-noise ratio value. In addition, the experimental results show that by using the proposed re-shifting and extraction formulas, the technique has the ability to extract the hidden data and retrieve the original images from the stego images. In comparison to the traditional histogram-shifting techniques, the proposed technique significantly improves the stego image quality and the embedding capacity. Thus, this research has contributed to two principles, namely improvements in capacity and quality