It's been used way before the nsfw stuff and the advent of AI.

Back in the days if you were doing an AMA with a celeb, the picture proof is the celeb telling us this is the account they are using. Doesn't need to be their account and was only useful for people with an identifiable face. If you were doing an AMA because you were some specialist or professional, giving your face and username doesn't do anything, you need to provide paperwork to the mods.

This is a poor way to police fake nudes though, I wouldn't have trusted it even before AI.

It used to be tits or GTFO ON /b.

From now on I'll have amazing tits.

Probably not, but it would still reduce the amount considerably.

I think it takes a considerable amount of work to photoshop something written on a sheet of paper that has been crumpled up and flattened back out.

It's mostly about filtering the low-hanging fruit, aka the low effort trolls, repost bots, and random idiots posting revenge porn.

there's a lot of tools to verify if something was photoshopped or not... you don't need to be an expert to use them

From reading the verification rules from /r/gonewild they require the same paper card to be photographed from different angles while being bent slightly.

Photoshopping a card convincingly may be easy. Photoshopping a bent card held at different angles that reads as the same in every image is much more difficult.

Jut ask for multiple photos of the person in the same place, AI has a hard time with temporal coherence so in each picture the room items will change, the face will change a bit (maybe a lot), hair styles will change... etc