FDCT-based watermarking for robust and imperceptible medical image protection

Security in medical imaging is a pivotal concern within the healthcare domain, prompting exploration into various watermarking techniques designed to embed imperceptible and secure data within medical images. In this study, we introduce a frequency-based medical image watermarking approach that leverages the Fractional Discrete Cosine Transform (FDCT), Mellin Transform, and Schur decomposition to extract the frequency content of the image. This process is followed by the selection of low-frequency coefficients for further transformation using Schur decomposition. The integration of watermark bits occurs through modulation of the obtained Schur coefficients, ensuring robust and secure watermarking without significantly altering the visual quality of the medical images. The experiments conducted on the ocular database illustrate the capacity, imperceptibility, and robustness of the proposed method. The proposed approach achieves a PSNR of 39.38 dB and SSIM of 0.9998, demonstrating excellent imperceptibility with a capacity of 0.07031 bits per pixel (BPP). The method is robust against various attacks, including JPEG compression, noise addition, and geometric transformations, with NCC values consistently above 0.85 for most common image processing operations. This approach successfully achieves a favorable trade-off between imperceptibility and information embedding capacity, ensuring the authenticity and integrity of medical images during transmission.