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Anthropic ships a browser-local C2PA checker for files made with Claude, and is explicit about what it cannot tell you
claude.com/check-content, which reached Hacker News on 2026-09-02, lets you drag in a file and read its content credential without the file leaving the browser, supporting JPG, PNG, GIF, WEBP, TIFF, HEIC, AVIF, SVG, DNG, JXL, MP4, MOV, AVI, WAV, MP3, M4A and FLAC up to 100MB. Anthropic describes two separate mechanisms: text carries a watermark in the writing itself, while files get a signed C2PA provenance note attached on download. The honest caveat in their own copy is the useful part for builders, that the tool only detects the credential, so it tells you whether Claude was involved in producing the file and not whether Claude created the content.
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