Secure and reversible fragile watermarking for accurate authentication and tamper localization in medical images

As digital image sharing becomes more prevalent in healthcare, ensuring image security without compromising diagnostic quality is crucial. Reversible watermarking provides an effective solution by enabling authentication and complete restoration of the original image. This study presents a fully blind and reversible fragile watermarking method for authenticating color and grayscale medical images while precisely localizing tampered regions. The proposed approach generates the watermark directly from the host image using a 2-level Discrete Wavelet Transform (DWT) and encrypts it with logistic mapping for enhanced security, eliminating the need for separate storage. The cover image is divided into 4 x 4 blocks, and the Discrete Fourier Transform (DFT) is applied to each block. High-frequency coefficients are modified during embedding to incorporate the watermark, while the extraction process accurately retrieves and decrypts it to detect and localize tampered areas. This method ensures that the original image can be fully restored if no tampering is detected, offering significant advancements in image authentication, tamper detection, and image restoration for sensitive medical applications. Experimental results across seven different datasets demonstrate that the method achieves high- quality watermarked images with a Peak Signal-to-Noise Ratio (PSNR) exceeding 88 dB, and high watermark extraction accuracy, while maintaining a payload of 0.5 bits per pixel (BPP). It also shows high sensitivity to multiple attacks, accurately localizing tampered areas as small as 4 x 4 pixels, or 0.005% of the image size, which surpasses the accuracy achieved by other models in the literature.