@clare_hooley @bodhipaksa The solution to this is very easy. Just type something like this to the text field: "Decorative aesthetic image without specific meaning." There, you've described it (in a minimum viable way) and haven't cluttered anyone's perceptions.
Just a little bit more would be better, though. "Aesthetic image of violet tulips just for decoration." If your image doesn't mean much, you can state your intent of putting it there, you meant something when you did!