In this particular piece, we see that apparently Mr. Uccello's a Tauren Druid. Who knew? Check out the rest of the set, they're wonderful!
[UPDATED: paulthewineguy has taken all the photos off his Flickr page. He states 'I reckon I've made a mistake, i.e. modifying pieces of art with no right whatsoever of doing so.' You can read the rest here.]