Digital Watermark Processing System Based on DCT Watermarking Algorithm

In digital watermark processing systems, the workflow primarily includes two processes: watermark embedding and watermark detection. The watermark embedding process combines the digital watermark (X), original image (I), and key/public key (K) through a digital watermark embedding algorithm to generate the watermarked image (I*). In implementation, this typically involves applying DCT transformation to image blocks, identifying significant coefficients based on magnitude thresholds, and modifying these coefficients using additive or multiplicative embedding rules with the watermark sequence. During watermark detection, the digital watermark (X), watermarked image (I*), and key/public key (K) are processed through a digital watermark detection algorithm to verify the presence or integrity of the watermark. The system employs a DCT-based watermarking algorithm that embeds a random sequence as the watermark signal into the magnitude components of significant DCT coefficients, where the top n coefficients with the largest magnitudes are selected as significant components. The algorithm implementation typically includes coefficient sorting mechanisms and embedding strength control parameters. Additionally, we define a similarity function, often implemented as correlation coefficient calculation or normalized cross-correlation, to validate successful watermark extraction. Experimental results demonstrate that this algorithm not only maintains imperceptibility but also exhibits considerable robustness against common image processing operations such as cropping, scaling, median filtering, compression, and noise interference. This robustness is achieved through strategic coefficient selection and embedding strength optimization in the frequency domain. The algorithm's performance characteristics make it suitable for applications in image copyright protection and authentication systems, where both visibility constraints and attack resistance are critical requirements.