It’s not 100% foolproof everytime, but since the core technology generative AI uses is denoising, that leaves artifacts you can spot if you look hard enough. Think of it like the process of remembering a dream: what AI creates has the look of someone trying to remember a place from memory, so it messes up little details that it’s trying to fill in, versus art made by humans, where every piece of the visual space had time, effort and thought put into crafting details. There’s always an unintentionality to AI pieces that isn’t present when a human is creating it.

You can really see this if you poke around Art Station and DeviantArt in the sci-fi concept art category. You’ll see pieces where every bit of the giant space machine makes visual sense: no crossed perspective lines, wires that don’t actually connect, people in the background have the right number of limbs and are in realistic poses.