1908 HONUS WAGNER batting lefty by G.G. BAIN

The only known photo of Wagner batting lefty. Also in the picture is HOF catcher Roger Bresnahan.

http://www.earlyerabaseballphotos.com/8xphhowarobr.html
http://www.halfwaytoconcord.com/honus-wagner-batting-left-handed/
http://90feetofperfection.com/2011/03/12/mr-baseball-bartell-vs-hartnett-pudge-the-flying-dutchman-the-say-hey-kid/
Also, read the last paragraph about Wagner here:

http://news.google.com/newspapers?nid=888&dat=19520217&id=34paAAAAIBAJ&sjid=ME8DAAAAIBAJ&pg=2047,525889

The same note that a reviewer makes about his biography:

"Although there is a tendency to think that Wagner could hit any pitcher who ever lived, he tells of one hurler, Jack Taylor, who gave him more trouble than any other. So much trouble, that Wagner once turned around and batted left-handed against the right-handed Taylor. Although Wagner says he "swung like a woman" he also punched the ball over the first base bag for a double. Other anecdotes include the time Jack Murray of the Giants made a game-saving catch by a flash of lightning, a bit on the game (and the box score) that clinched the 1901 pennant, Bill Klem tossing Clarke from a game for saying he was "a model umpire," and much more."