More on the topic…
Claude embeds markers into files it creates so you can verify their origin. Images and documents get a cryptographic signature embedded in their metadata—basically a tamper-proof note saying Claude made or edited the file. Text gets watermarked differently, directly in the writing itself. The tool on this page checks for those file credentials specifically. It won't tell you whether Claude actually generated the content inside (just that Claude touched the file), and it doesn't reveal anything about who used Claude to make it.
The credential system uses C2PA, an open standard that camera makers and photo software already use to track image provenance. Any tool that reads C2PA can spot Claude's signature. Other AI companies like OpenAI and Google have similar detection tools for their own outputs. When you upload a file to check, the tool only reads that embedded credential—it doesn't scan the actual content, store your file, or use it for anything else. Your file stays on your device the whole time.
For detecting whether Claude wrote text, Anthropic has a separate Detection API that's currently limited to certain organizations in the EU where the law requires it. The company's documentation goes deeper into both file and text detection methods if you want the technical details.
Questions about this article
can this just be circumvented by resaving a file into a new file?
Yes, resaving a file into a new file would likely circumvent this detection, because the credential is metadata embedded in the file itself. When you resave or export a file, most applications don't preserve metadata from the original—they create a fresh file with only the content, stripping out any embedded credentials in the process.
From the article, the checker works by reading "the embedded credential, not the file itself." That credential is "a small, cryptographically signed note in the file's metadata" attached when Claude creates the file. The moment you resave that file—whether through export, screenshot, copy-paste into a new document, or format conversion—you're creating a brand new file without the original metadata intact.
This is a known limitation of metadata-based detection systems generally. While the [C2PA standard](https://c2pa.org/) (which Claude uses) is designed to be robust, it only works if the metadata travels with the file. Most software doesn't automatically preserve or re-sign credentials when you manipulate or re-export files.
So yes, someone determined to hide the origin of AI-generated content could easily do this. It's one reason why metadata-based provenance alone isn't foolproof—which is probably why Anthropic also mentions they have a separate text watermarking system (though the article notes that's currently in private preview for detecting watermarks in text specifically).