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GregFor a pretty good reference to the history on uniforms over the years, go to the National Baseball Hall of Fame's website. You can do a search for many teams.
Here is a link for Pittsburgh, which backs up Barry's opinion on dating the photo to 1916:
http://www.baseballhalloffame.org/exhibits/online_exhibits/dressed_to_the_nines/uniforms.asp?league=NL&city=Pittsburgh&lowYear=1901&highYear=1950&sort=year&increment=18
Hope this helps,
Greg