Secure and Invisible Dual Watermarking for Digital Content Based on Optimized Octonion Moments and Chaotic Metaheuristics

In the current digital context, safeguarding copyright is a major issue, particularly for architectural drawings produced by students. These works are frequently the result of innovative academic thinking combining creativity and technical precision. They are particularly vulnerable to the risk of illegal reproduction when disseminated in digital format. This research suggests, for the first time, an innovative approach to copyright protection by embedding a double digital watermark to address this challenge. The solution relies on a synergistic fusion of several sophisticated methods: Krawtchouk Optimized Octonion Moments (OKOM), Quaternion Singular Value Decomposition (QSVD), and Discrete Waveform Transform (DWT). To improve watermark embedding, the biologically inspired algorithm Chaos-White Shark Optimization (CWSO) is used, which allows dynamically adapting essential parameters such as the scaling factor of the insertion. Thus, two watermarks are inserted at the same time: an institutional logo and a student image, encoded in the main image (the architectural plan) through octonionic projections. This allows minimizing the amount of data to be integrated while increasing resistance. The suggested approach guarantees a perfect balance between the discreetness of the watermark (validated by PSNR indices > 47 dB and SSIM > 0.99) and its resistance to different attacks (JPEG compression, noise, rotation, resizing, filtering, etc.), as proven by the normalized correlation values (NC > 0.9) obtained following the extraction. Therefore, this method represents a notable progress for securing academic works in architecture, providing an effective, discreet and reversible digital protection, which does not harm the visual appearance of the original works.