When automated detection fails then it's up to people to manually report it and mods / admins to manually apply the label.
Which is not reliable, and which therefore leads to the witch-hunting problem.
Whether an image actually is AI and whether some random person thinks it "looks" AI are not always in alignment. Especially considering that "is AI" has shades of grey too, given that lots of images are made using AI tools for only some aspects. And even "AI tool" is open to interpretation.
I was talking about screening and reporting posts and you've moved to profile pics for some reason?
It was just an example of an AI-generated image that I could point to that I'm quite sure doesn't have any special metadata attached to it. If for no other reason than I generated it years ago.