That is really amazing! It is a different spin to those shadow pictures that people make on the walls, using their hands. That takes a great imagination!
I should think you'd have to be ambidextrous in order to do anything like this. I could probably paint my left hand quite nicely but when it came time to do my right, it would look like a 5-year old did it! Of course, my artistic abilities would be left behind trying to be as detailed as those photos show. That would be amazing work on canvas, let alone on hands.