Anthropic Releases a C2PA Verifier for Claude Files

Key Takeaways

1Anthropic launches a web tool to check for the presence of a C2PA signature on files generated by Claude

2The tool works in the browser, without transferring files to Anthropic, and provides a binary verdict

3Supported formats: images (JPG, PNG, GIF, WEBP, TIFF, HEIC, AVIF, SVG, DNG, JXL), videos (MP4, MOV, AVI), audios (WAV, MP3, M4A, FLAC), size limited to 100 MB

4The marking does not guarantee that the content was created by Claude and does not identify the user; the text watermark remains accessible only via a restricted API

Why it matters : This device illustrates the current limitations of automated detection of AI-generated content and the caution needed in interpreting the results.

Anthropic has proposed an online tool to confirm whether a file carries the C2PA signature added during upload from Claude. The company outlines its usage: compatible formats, maximum size, and the scope of the marking, which is distinct from the text watermark detectable only via a restricted-access API.

Conditional Verification and Limited Scope Announced by Anthropic

Anthropic clarifies that the signature embedded in files only attests to Claude's involvement in production, without guaranteeing that the content was created by Claude, and it does not contain any data that could identify the user. The company also notes that the absence of detection does not necessarily mean that Claude was not used, as the content credential markers can disappear if the file is edited, converted, or compressed; thus, the result depends on the exact version of the analyzed file. Supported files must not exceed 100 MB. Since 2023, numerous tools for detecting AI-generated content have been launched, none of which guarantee consistent reliability.

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A Web Tool That Provides a Binary Verdict on the Presence of the Credential

Publicly presented on September 2, the tool "Check if a file was made with Claude" can be used directly in the browser and, according to Anthropic, does not transmit any files to its servers. The user simply needs to import a file to receive a binary response indicating whether the signature is detected or not. The tool does not provide any information about the text of the file; its role is limited to verifying the signature embedded in the metadata.

Supported Formats: Images, Videos, and Audios Listed

The verifier supports several formats. For images: JPG, PNG, GIF, WEBP, TIFF, HEIC, AVIF, SVG, DNG, and JXL. For video: MP4, MOV, and AVI. For audio: WAV, MP3, M4A, and FLAC.

Two Distinct Markings: C2PA Metadata and Text Watermark

In mid-August, Anthropic introduced two complementary approaches. Uploaded files receive a content credential, a cryptographically signed note embedded in the metadata, based on the open standard C2PA already used by some camera manufacturers. The generated texts are marked by a watermark that modulates word choices during generation and remains undetectable without a key. Detection of this text watermark is done through an API reserved for certain organizations.