I have the impression that the lion’s share of all posts on Lemmy are reposts or screenshots from other platforms. I don’t mean links to other sites of course, after all Lemmy is a Reddit clone and thus a link aggregator. I just think that Lemmy can’t survive if there is no way to make people aware that a particular post is OC to a fediverse-Plattform. I suspect that the Lemmy community would appreciate the effort that went into creating OC that wasn’t posted anywhere else - there’s just no way to tag Lemmy OC.
I’m pretty sure that everybody at !imageai@sh.itjust.works is posting original content. I am. Nobody’s going to bother to tag it, though – it’s just the default.