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EU AI Act · Article 50(2) · Synthetic content
How do I mark AI-generated content under Article 50(2) — and prove the marking held?
What Article 50(2) requires
Article 50(2) places the obligation on providers of generative AI systems: outputs (synthetic audio, image, video, or text) must be marked in a machine-readable format and be detectable as artificially generated or manipulated. The technical solutions must be effective, interoperable, robust and reliable as far as is technically feasible. These obligations apply from 2 August 2026.
Watermarks, metadata, and C2PA manifests are ways to apply the mark. None of them, on their own, prove to a third party that a given output was marked at the moment it was generated — which is what a dispute or an audit turns on.
The evidence gap: a mark can be stripped or contested
Metadata gets removed on re-encode. Watermarks get cropped. When a specific piece of content is challenged — “was this actually marked, or added later?” — you need an independent record that the marking existed at generation. A tamper-evident receipt closes that gap:
| Property | Screenshot / self-written log | Tamper-evident receipt |
|---|---|---|
| Independently checkable | No — requires trusting you | Yes — anyone can verify |
| Tamper-evident | No — editable in place | Yes — any change is detectable |
| Timestamp you can't backdate | No — system clock | Yes — cryptographically anchored |
How to produce the evidence
- Capture the event. At the moment the disclosure, marking, or label is applied, record the exact text or marking, the output's content hash, and the context.
- Fingerprint it. The SDK computes the SHA-256 fingerprint locally — the content never leaves your systems (hash-only, GDPR- and confidentiality-clean).
- Anchor it. Fingerprints are folded into daily RFC-9162 Merkle roots and anchored to the public chain via a public-ledger transaction.
- Verify it — anytime, by anyone. Re-check the receipt against the public chain with the open-source verifier, no account required.
Because the receipt format is an open IETF Internet-Draft implementing the SCITT architecture, the evidence you hold today keeps verifying even if any single vendor disappears.
Anchoring doesn’t replace your marking mechanism — it makes it provable. The watermark or C2PA manifest is the label; the anchored receipt is the independent proof that this exact output carried that label at that time. See the general Article 50 evidence guide for how the obligations fit together.
Frequently asked questions
Does anchoring a receipt replace watermarking or C2PA?
No — it complements them. Watermarking and C2PA are how you apply the machine-readable mark Article 50(2) asks for. An anchored receipt is the independent proof that a specific output carried that mark at generation time, which survives even if the watermark is later stripped or the claim is disputed.
What counts as machine-readable marking under 50(2)?
The Act calls for outputs to be marked in a machine-readable format and detectable as artificially generated or manipulated, with solutions that are effective, interoperable, robust and reliable as far as technically feasible — for example embedded watermarks, cryptographic provenance (C2PA), or metadata. LedgerProof does not judge which mechanism satisfies the Act; it produces verifiable evidence that whichever mechanism you used was applied.
Does this send the generated media anywhere?
No. LedgerProof anchors only the SHA-256 fingerprint of the output and the marking record. The media itself never leaves your systems — hash-only, GDPR- and confidentiality-clean.
When does the obligation apply?
Article 50 transparency obligations apply from 2 August 2026. Anchoring evidence as you generate content from now on means the proof already exists when a specific output is later challenged.
Last updated 1 August 2026 · LedgerProof