I don't know if you were aware of this feature, but it's possible to permanently ban users by selecting "Other time:" from the drop-down menu in the Expiry field and then typing "infinite" or "indefinite" in the field under that.
Obviously, we don't want to do this to anonymous editors (i.e. those identified by their IP address), but it's a good way to deal with named users who have no interest in making meaningful contributions to the wiki. That's what I've been doing to users like UgliestGrannyAboriginal/HotBlackWoman/BlackMonkeyCriminal who create accounts solely to upload pictures and vandalize as many articles as possible. It's pretty pathetic that some people have nothing better to do with their time than post nonsense and racist screeds onto wiki articles, but I don't see much we can do about it aside from dealing with the problems as they arise.