If you need a free online tool to strip watermarks out of photos as fast and accurately as possible, Dewatermark is a good choice. The tool uses AI technology to spot and remove even sophisticated watermarks in photos. It's got some manual editing controls, and it preserves image quality well, so it's good for serious use in school, research and publishing.
Another good option is WatermarkRemover, another AI-powered tool that works with many file formats. It's got a bulk conversion option and an API for automated integration, too, so it's good for personal or professional use. The tool is easy to use and preserves image quality, so it's a good option if you need to strip out watermarks quickly.
If you want a broader range of tools, check out HitPaw Online. This suite of AI-powered tools includes background removal, image watermark removal and video editing. It's got a free version with limited uses, but you can pay for subscription plans with more downloads and processing.