well, Theres still plenty telltale signs of AI handwork here. Quasi-faces on places no human would place them or would articulate a detail much better. edge coherence is also very important. Seeing smudges of paint where it doesn't belong at all, lines no human would be able to make and errors only humans make but where AI struggles with.

My point is that Dalle can do things like the Cornell box pretty much perfectly, so if you want to make a test where it's impossible to decide who made it you should sample those type of prompts.