Cool action shot on that Greenberg PC.
This looks like a Jim Rowe postcard made from a George Burke photo negative. Any PC with that Kodak stamp box on the back would have been produced after 1950. So while the image is likely from the 30's to 40's, the postcard wasn't produced until likely the 60's-70's. I believe the writing on the back that shows "Greenberg" is consistent with many other Rowe PC's I've seen before.
Good discussion on Rowe postcards here:
http://www.net54baseball.com/showthread.php?t=118709
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http://imageevent.com/derekgranger
HOF "Earliest" Collection (Ideal - Indiv): 244/342 (71.4%)
1914 T330-2 Piedmont Art Stamps......: 114/119 (95.8%)
1923 V100 Willard's Chocolate............: 177/180 (98.3%)