Taken by an unknown photographer, this is Señor Romualdo Saeriz, the “Crack Shot of Mexico,” 29, n.d.
Photographic Postcard. Collection of Mexican Revolution (1910-1920) photographs, Collection 026. UCR Library, Special Collections & University Archives, University of California, Riverside.
Source: kcet.org ← a most interesting article with many more fabulous photos.