Digital libraries, as information resource sharing platforms, face severe challenges of data security and copyright protection. In this paper, we propose a DCT-Schur based digital watermarking encryption scheme to realize the security protection of digital resources through the combination of discrete cosine transform, Schur matrix decomposition and Logistic chaotic mapping. The scheme constructs the watermark embedding process from six links: watermark preprocessing, DCT transform, carrier image chunking, Schur matrix decomposition, watermark feature embedding and carrier image restoration, and controls the extraction and decryption restoration of watermarked signals through key sequences. The experimental results show that the scheme has good invisibility, and the PSNR values of the images after embedding the watermark are all greater than 45.0 dB, and the SSIM coefficients are all more than 0.993. In terms of robustness, the scheme can effectively resist all kinds of attacks, and the NC value of the extracted watermark still reaches 0.9663 even under the attack of rotating 10°; the NC value under the attack of shearing 1/4 stays above 0.9908, which is significantly better than the existing methods. This scheme performs well in balancing watermark invisibility and robustness against attacks, and provides an effective solution for data security design and copyright protection in digital libraries.
