Towards a robust and fully reversible image watermarking framework based on number theoretic transform

This paper presents a new watermarking approach in the spectral domain based on the number theoretic transform (NTT) to ensure sharing and transferring medical images in a secure way. Through this approach we ensure also the robustness of the embedded watermarks within the medical image to prove ownership. The NTT's effectiveness has been proven in the images lossless transmission and in convolution fast calculation. In this new approach, the watermark is embedded into the NTT image based on linear interpolation with a specific factor controlling the visibility/invisibility of the watermark. The extraction process will be performed on the attacked watermarked image in order to extract the attacked watermark. We are particularly interested in the NTT since it is considered as a fully reversible transform without any loss when choosing the suitable parameters. We measured the robustness of the proposed approach by the commonly used metrics against several scenarios of attacks (geometric and non-geometric) such as JPEG compression, adding noise, rotation, median filtering, etc. The tests are performed on several types of medical images. The obtained results are very encouraging and represent a remarkable robustness which will be detailed in this paper.