Abstract
This paper proposes a robust digital image watermarking scheme that integrates block-based Singular Value Decomposition (SVD) with a three- level Discrete Wavelet Transform (DWT) preprocessing stage applied to the watermark. The host image is partitioned into non- overlapping 16×16 pixel blocks, with SVD applied independently to each block, while the watermark is decomposed through three successive Haar wavelet levels to yield a compact 32×32 approximation subband (cA3) whose 1024 elements align precisely with the 1024 image blocks in a lossless one- to- one mapping, eliminating the resizing- induced information loss characteristic of conventional hybrid schemes. Each watermark coefficients is embedded additively into the dominant singular value of its corresponding block, and extraction is accomplished in a semi- blind fashion using the stored SVD components and DWT detail subbands as secret keys. Tests on standard benchmark images show that the proposed scheme yields an average PSNR of roughly 50 dB and an SSIM close to 1, indicating that the embedded watermark is practically invisible. When subjected to eight common signal- processing attacks, the scheme reaches a normalized correlation of 0.9657 after JPEG compression, which exceeds the compression robustness reported for earlier SVD- based and hybrid DWT-SVD watermarking methods, and it remains competitive under filtering and noise attacks. These results support its use for copyright protection of digital images.