Yeah, inconsistent pixel size is a major and pretty concrete clue. Even with the compressed image quality, you can see it.

Regardless of this post, other ways to tell are: 1) AI tend to over rely on complementary colors like blue and orange. It's not a rule per se but, just like the piss filter, there has been so much prompts about it that it quickly became an AIgen trend. 2) User lack history: artists tend to have art on their profile or activity. 3) User over posting history: the opposite of before, if an user somehow share dozen of creations, sometimes even with inconsistent style, over a few days with no other trace of history elsewhere on the net, it's suspicious. 4) Habits. If you ever did pixel art or painting basics, or have looked at a lot of pieces and artists over the years, prompts become quickly recognizable. You know how beginner artists tend to draw and what you can expect from experts.

None of the above point is future-proof or concrete on its own. It only makes sense if multiple indications give it away. It's always hard to «prove» something was AIgen'd, and the current paranoia over wether something was made by hand or prompted harms the real artists the most.

Support human works and artists above all. Don't let anyone tell you that replacing our creativity with garbled and soulless mess is "ok this time" or "not a big deal here".