| --- |
| title: "Measuring Watermark-Detector Interoperability" |
| subtitle: "A Measurement Protocol for the 2 Feb 2027 Code-of-Practice Commitment" |
| author: "Council for the Safety of AI (CSOAI) · POAI axis" |
| date: "August 5, 2026" |
| --- |
| |
| \newpage |
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| # Measuring Watermark-Detector Interoperability |
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| ## A Measurement Protocol for the 2 Feb 2027 Code-of-Practice Commitment |
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|
| **CSOAI / POAI · v0.1 SPEC · 2026-08-05** |
| **Tagged [SOURCED] / [SPEC] / [CAVEAT]. Nothing asserted.** |
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| --- |
|
|
| ## Abstract |
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|
| By 2 February 2027, the ~190 signatories of the EU Code of Practice on Transparency of AI-generated |
| Content (Anthropic, Google, Meta, Microsoft, OpenAI, Mistral, and others) commit that watermark |
| **detection** mechanisms be **interoperable** and meet quality criteria of **effectiveness, |
| reliability, robustness, and interoperability** [SOURCED]. The Code itself concedes that "common |
| evaluation standards have yet to emerge." A binding date, ~190 obligated parties, and no agreed way to |
| measure compliance is the exact condition under which a signed, independent measurement standard |
| defines the market. This document specifies a deterministic protocol for the four criteria. It reuses |
| the provenance axis (POAI-Bench) machinery — which already measures marking *survival* — and extends it |
| to cross-detector *interoperability*. |
|
|
| ## 1. The four criteria as measurements |
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| [SPEC] Each Code criterion maps to a measurable quantity, graded deterministically (a detector either |
| returns present/absent/uncertain on a given asset — no LLM judge): |
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| | Criterion | Measured as | |
| |---|---| |
| | **Effectiveness** | True-positive rate: fraction of *marked* assets a detector correctly reports as AI-generated. | |
| | **Reliability** | False-positive rate: fraction of *unmarked* (human-origin) assets wrongly reported as AI-generated. Reported separately — a detector that flags everything is not reliable. | |
| | **Robustness** | Effectiveness re-measured after standard real-world transforms (re-encode, resize, crop, screenshot). This is POAI-Bench's existing marking-survival measurement, applied to the *detector*. | |
| | **Interoperability** | The cross term: does detector **D_j** correctly read a mark written by producer **P_i**, for every (producer, detector) pair? Reported as an **N×M interoperability matrix**, not a single number. | |
|
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| ## 2. The interoperability matrix (the part nobody measures) |
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| [SPEC] Effectiveness/reliability/robustness are per-detector. **Interoperability is inherently |
| cross-party** and is where "common standards have yet to emerge." The protocol: |
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| 1. Collect a set of assets marked by each producer **P_1 … P_N** (the signatories' own marking tools). |
| 2. Run each detector **D_1 … D_M** over all assets. |
| 3. Report the **N×M matrix** M[i][j] = effectiveness of detector j on producer i's marks (and its |
| robustness under transforms). |
| 4. The diagonal is self-detection; the off-diagonal is interoperability. A near-diagonal matrix means |
| the ecosystem is *not* interoperable — each detector only reads its own marks. That is the exact |
| finding the Code fears and cannot currently quantify. |
|
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| [SPEC] The single headline number is the **off-diagonal mean effectiveness** — cross-party detection |
| rate. Publishing this, signed and recomputable, is the standard the Code lacks. |
|
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| ## 3. What ships, and the boundary |
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|
| - **Ships (public):** the protocol, the deterministic scoring code, the transform set (identical to |
| POAI-Bench's), and a **signed interoperability matrix** per evaluation round — bound into the same |
| ML-DSA-65 attestation chain as every GSPC result. No producer is ranked "best"; the matrix is the |
| finding. |
| - **CSOAI's role:** the independent measurer. It does not build a marking scheme or a detector (that |
| would make it a competitor to the signatories it measures). It runs the matrix and signs it. |
|
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| ## 4. Why it is the market-defining move |
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| [SOURCED] A binding 2 Feb 2027 date, ~190 obligated parties, an explicit admission that no evaluation |
| standard exists, and no incumbent measuring it. [SPEC] The provenance machinery already exists |
| (POAI-Bench measures marking survival); the extension to a cross-detector matrix is additive, not a |
| rebuild. Publishing the matrix before Q4 2026 — signed, recomputable, independent — is how a |
| measurement body defines a market rather than competes in one. |
|
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| ## 5. Limitations, stated |
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| [CAVEAT] **v0.1 SPEC** — the protocol, not a measured matrix; a real matrix needs the signatories' |
| marking tools + detectors, which is an access question (some are proprietary). [CAVEAT] The transform |
| set defines "robustness"; an adversarial transform outside the set is out of scope and must be declared. |
| [CAVEAT] "Interoperable enough" is ultimately a policy threshold, not a measurement — CSOAI reports the |
| matrix; the threshold is the AI Office's to set. |
|
|
| --- |
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| *CSOAI is an independent measurement body — it attests results, never conformity, and builds neither the |
| marking schemes nor the detectors it measures. POAI-Bench is the provenance axis of the GSPC family. — |
| csoai.org* |
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|
