I've been seeing many images (particullary from final_fantasy_xiv though I am sure there are other copyrights with this same issue) tagged with the name of the characters the image is from. (Example: janelle_colbernoux)
What is to be done in this case? Delete the char tag? Being there aren't really characters from the game lore itself nor do they have an obscene amount of pictures as to "earn" a tag I do think they shouldn't be tagged at all. Yet I want to get an opinion on the matter before making corrections on such pictures.

Is there a compelling reason why recurring named characters shouldn't be tagged? We have dozens of tags for original characters and their existence doesn't seem to have caused us any problems yet. Removing any such tags would be a loss of information that, while maybe not useful to you in particular, may still be useful to someone else.

If it's an OC made to be inserted into an official franchise, it's not really a part of that franchise. It could make it difficult for someone to leaf through artwork for that franchise if they don't want to be spammed with mary sues and sonichus. They're not inherently bad, but they can clutter search results with irrelevant content, and misrepresent the franchise.

Maybe not outright removing them, but unlike the OCs iridescent slime listed, the example FeKa gave doesn't have any labeling to indicate it's an OC. I'd think ensuring that tag is there would allow people to filter them out if desired.

check this out: final_fantasy_xiv -original

In FFXIV's case, most original characters really seem to be depictions of customized player characters. Is there grounds to create player_character_(ffxiv), like with admiral_(kantai_collection)?

The example I've given is a picture of a person's character (You can search it in the FFXIV Lodestone). Most I've seen were this case unlike characters like altera_moontail for example in FFXIV case or monara for WoW. I do agree it isn't something as terrible as we have dozens of original characters already, yet on the other hand, if everyone is going to tag their characters name in every fanart made... IMO a tag should be used when there's a good amount of that character art. I really doubt that any random person will search for just a random PC from any game. I do like the idea of having a general tag for this kind of situation as the poster above me suggested though.