The text watermarking is the more interesting problem here. Image watermarking is fairly tractable - you can embed a robust signal in spatial or frequency domains. Text watermarking works by biasing token selection at generation time, and detection is a statistical test over that distribution.

Which means short texts are basically useless. A 50-token reply has too little signal for the test to reach any confidence. The original SynthID text paper puts minimum viable detection at a few hundred tokens - so for most real-world cases (emails, short posts, one-liners) it just doesn't work.

The other thing: paraphrase attacks break it. Ask any other model to rewrite watermarked text and the watermark is gone, because you're now sampling from a different distribution. EU compliance built on top of this feels genuinely fragile for anything other than long-form content from controlled providers.