Even if there were tools that can dictate what is AI-generated and what not, they’d have to rely on a pattern, or on an artifact from AI-generated imagery (which, as far as I know, does not exist), and that is what can be used as proof, not the result of the tool itself being used.
But then, it begs the question, how would you prove it’s an AI work? For all anyone knows, it’s my art, I made it, it’s undistinguishable from what I could make. What the court will see is, I submitted that art in the Internet, you take that, I sue you for copyright, you argue it’s an AI work, and the Court will request you to prove it really is an AI work, and perhaps launching an investigation on me to see whether I really made the AI artwork.