If you are sued for infringement on someone else's copyright, the fact
your image doesn't have any is not relevant, what is relevant is if you
did infringe or not on the copyright on the image of the other party.
Besides, that statement of OpenAI seems rather to mean that *they* don't
claim copyright on the output, not that you as the user can't (try to)
claim copyright.
And whether you as the user (person instructing the AI) can claim
copyright on the image is legally unclear, though on a recent case in
Germany, the court ruled that AI generated images are not copyrightable.
So, within the EU that is now case law, but that could change,
especially as case law tends to be reinforced, refined, or torn down
with more cases on the subject.
Mark
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Mark Rotteveel