Digital image watermarking is a vital tool for copyright protection and content authentication. However, most existing methods perform well only under single noise types, while real-world applications often involve composite noises with multiple distortions, leading to poor robustness. To address this issue, we propose a robust image watermarking scheme. To improve performance under combined noise conditions, a two-stage training strategy is introduced: in the first stage, noise intensity increases gradually to stabilize training; in the second stage, mixed strong noises are applied to enhance generalization against complex attacks. Specifically, a strength-balanced watermark optimization algorithm is employed during the testing stage to improve visual quality while maintaining strong robustness. Furthermore, to improve robustness against JPEG compression, we adopt a differentiable fine-grained JPEG module that accurately simulates real compression and enables gradient backpropagation during training. Experimental results demonstrate the superiority of the proposed method under various single and combined distortions. Under noise-free conditions, it achieves 0% bit error rate and 53.55 dB PSNR. Under composite distortions, our scheme maintains a low average BER of 2.40% and a PSNR of 42.70 dB.

Fuzzing deep learning (DL) libraries is essential for uncovering security vulnerabilities in AI systems. Existing approaches enhance large language models (LLMs) with external knowledge such as bug reports to improve the quality of generated seeds. However, most approaches still rely on static strategies or single knowledge sources, limiting their ability to produce syntactically valid inputs that also expose deeper bugs. To address this challenge, we propose an adaptive seed generation approach that models knowledge-guided prompt selection as a multi-armed bandit problem. Our method first constructs two knowledge bases from API documentation and bug reports, then dynamically selects and refines prompt strategies based on real-time feedback. These strategies are tailored to the knowledge types in the respective bases. We design a multi-dimensional reward function to evaluate each batch of generated seeds by measuring their error-triggering potential and behavioral diversity, enabling a balanced exploration of both syntactically valid and bug-triggering test cases. Our experiments on three DL libraries, PaddlePaddle, MindSpore, and OneFlow, identify 17 previously unknown crash bugs, demonstrating the effectiveness and generalizability of the proposed approach.