I think the biggest problem is that reading no_humans at face value means exactly that. When I see a picture of Kirby scribbling on a sheet of paper, I see no humans there. Sure I see a round, pink character doing a normal human activity, but I still don't see a human.
So I think if we want the tag to exclude any possible human-like presence, it should reflect that notion better, something like no_one or nobody. This way, in the aforementioned Kirby example, there would be no humans present in the picture, but there wouldn't be nobody.