I would think that generating those images is okay by Disney, the same as if I painted them. The moment Disney would object is when I start selling them on merch, at which point it is irrelevant how they were created.
Am I mistaken?
The punishment for breaking any of these rules is a lot of people yell at you on Twitter. Unfortunately, they've been at it so long that they now think these are actual laws of the universe, although of course they have pretty much nothing to do with the actual copyright law.
That actual law doesn't care if you're selling it or not either, at least not as a bright line test.
(Japanese fanartists have a lot more rules, like they won't produce fan merch of a series if there is official merch that's the same kind of object, or they'll only sell fan comics once on a specific weekend, and the really legally iffy ones have text in the back telling you to burn after reading or at least not resell it. Some more popular series like Touhou have explicit copyright grants for making fanart as long as you follow a few rules. Western fanartists don't read or respect any of these rules.)