Just came across this site:
America's National Game: The Albert G. Spalding Collection of Early Baseball Photographs
It contains over 500 images of early baseball, circa 1874-88. Included is a very interesting photo of Chicago White Stocking pitcher
Charlie Sprague:
It's one of the few photos I've seen of a pitcher who appears set to deliver the ball underhanded. It's a posed photo in a studio, of course, but most photos of the time showed players throwing overhanded. Oddly, the photo is dated 1888, which suggests that Sprague was still pitching underhanded (or possibly sidearm) even though overhand pitching had been legal in the NL since 1884. Maybe that explains why he had such an undistinguished career in the majors.