This seems to occur every now and again, and I can't think of a good solution for it at all. If that character had an official name it could be used as an impromptu character tag, but since it doesn't I really have no idea what would make a good tag for it.
Some placeholder would be good though, at the very least...
Perhaps something akin to character_name_(cosplay), like artist_name_(style), artist_name_(derivative) or artist_name_(parody) -- it would be useful for borrowed characters as well as drawings done in a copied style.
