SignUnder's code is public on GitHub at AivaStack/signunder , under the Apache-2.0 licence, since 20 October 2026. It is the code the hosted service runs: the API, the C2PA signer, the watermark and fingerprint worker, the rules engine with its rule packs, and the .NET and Python SDKs.

SignUnder marks AI-generated images so the company that publishes them can show where they came from, under its own name, and meet labelling rules such as Article 50 of the EU AI Act.

What is in the repository?

The API (.NET 10): signing, verification, the registry of signed outputs, accounts and the public verify routes.

The signer (Rust), a thin gRPC service around c2pa-rs , the C2PA reference implementation, pinned to an exact version so the manifests it writes do not drift.…