They are not spymarks if they don't encode any personal IDs and are merely used to indicate that an image was AI-generated. I don't think Google or OpenAI use SynthID to include personal data.
And there lies the rub. You can't verify if they do or don't embed such content. These companies are just like "trust me bro".
Come on man, they're both advertising companies. Would you resist the opportunity to build that social graph and detect a known user anywhere on the internet?
>I don't think Google or OpenAI use SynthID to include personal data.
Why? I assume by default that it's uniquely identifiable, because it just makes practical sense for OAI and Google (tracking misuse at the very least, but also data), it's trivial to implement and trivial to hide or plausibly deny.