AI-generated images can still violate copyright, and all AI-generated images are dependent on having been trained on copyrighted materials.

So while I believe using AI-generated materials in your articles with proper credit as you've been doing is totally fine with the Medium rules and current US laws / court decisions, the latter could force the former to change in the future.

There are millions of non-commercial photos on Unsplash, and you probably have 1000s of photos in your own cloud storage, so I haven't seen any particular reason to bother waiting around for AI images to generate when I could find more useful, royalty-free photography faster.

But the easiest way to determine if AI photos are allowed by the rules are to see if you've been Boosted on Medium in any of those stories; Boosting (while rare) is about as big of a thumbs-up as you can get from the Medium rules.

That said, AI is allowed by the Medium rules:

"AI-generated or assisted images are allowed on Medium with the following provisions:

AI-generated images must include captioning identifying them as such. "

https://help.medium.com/hc/en-us/articles/22576852947223-Artificial-Intelligence-AI-content-policy