There are many that are near impossible to find and there have been multiple threads discussing the various opinions on who is toughest.
Here is one such thread, but there are a lot of them. Some have some great info in them. It would be well worth your time to do a search for them. They are very educational.
http://www.net54baseball.com/showthread.php?t=156413
If you were now to also add in that you want one on a photo, I think the list of unknowns probably gets much longer as many of the turn of the century and earlier players probably don't have one. The same goes for many of the Negro leagers and Cuban players.