John Wilkes Booth, the 26 year-old actor and later assassin of President Lincoln, was photographed many times over the course of his life. The numeration for his photographs is based on the 1979 book, John Wilkes Booth Himself by Richard and Kellie Gutman. Further information about these photographs can be found in their book.
LincolnConspirators.com 
He had a boney looking knee..
What was wrong with his knee? It looks deformed to me..
Books on John have mentioned that he was slightly bowlegged as a teen, which is where his nickname “Billy Bowlegs” came from.