A test for AI-generated art: railroad tracks. For some reason, none of the image generators can get railroad trackage even close to correct. Just getting long, parallel rails correct seems to be hard. Where there are multiple tracks, trains are positioned between tracks. Rail spacing, tie spacing, and clearances are all wrong. Two long parallel tracks without the rails getting mixed up is rare. Curves are wrong. Switches are hopeless.
There may be something about maintaining strong coherence all the way across an image that's hard for Stable Diffusion type systems. Iterated local refinement seems to botch this class of image.
Examples: [1][2][3][4][5][6]
[1] https://www.vecteezy.com/photo/37205933-ai-generated-high-sp...
[2] https://www.dreamstime.com/royalty-free-stock-photography-mo...
[3] https://www.magnific.com/premium-ai-image/high-speed-passeng...
[4] https://www.magnific.com/premium-ai-image/rail-yard-27_27291...
[5] https://www.magnific.com/premium-ai-image/train-track-with-s...
[6] https://pixabay.com/illustrations/ai-generated-train-tracks-...