The game also handles this(sending request), auto. When you search and search, there is a limit. "More pictures" and "more like this picture" eventually runs out of rolls(I estimate there are like 20-30 rolls per). So if you run out of rolls and didn't find something, probably is when it sends a request. To my understanding, the pics are already pre-generated, but hosted in Stardock's cloud or something, so you can't see them(like you know how they get a logo from the logo area but you can see which those are if you edit? Same principle.)
However you can tell a lot are AI generated, and some artist just refined them, or evaluated their usage(sometimes some bits remain, but there's so many and some are trully awesome, so it's negligible that some are a bit off and can be used anyway as flavor and minor civ gfx). There are categories of civ leaders now that weren't there before. But with the limitations, you might not come up with a pic you run into a second time soon. So if you find one you like save that and you can change the civ details later.
Also, the ACGPT algorithm seems off lately, generating less relevant pics, maybe due to the increased amount of pics? I asked for a creature and it gave me pics of anything but and loads robots. Then I asked for robot and it gave loads of creatures. I do expect they'll get hold of and fix it by release date, but there is still like what, 20 days for that?