Flexible Partial Screen-shooting Watermarking with Provable Robustness

Screen-shooting watermarking is an effective means of protecting screen content from unauthorized capture and illegal dissemination. However, existing methods are primarily designed for full-image capture, making them ineffective for partial screen-shooting prevalent in real-world scenarios. To address this limitation, we propose FPSMark, a flexible watermarking method tailored for partial screen-shooting that embeds consistent watermarks in multiple uniformly distributed cover blocks. Specifically, considering that robustness requirements vary according to the layout of each image, we model the mathematical relationship between the watermark block count and robustness, proving the flexibility of FPSMark in ensuring partial screen-shooting robustness. Moreover, partial screen-shooting disrupts watermark synchronization, posing challenges for precise watermark localization. To overcome this, we design an intrinsic signal localization network optimized with a hybrid loss. The localization network exploits the inherent distinctions between the watermark and non-watermark features, while the hybrid loss constrains the network at three dimensions: pixel-level, region-level, and sample-level. Experimental results demonstrate the superiority of FPSMark, showing robust performance across partial capture percentages. Its extraction accuracy exceeds 98% even with only half of the image captured, and it achieves 82% accuracy at a 40% capture ratio, whereas existing methods achieve only around 50% under the same conditions.