Allan Pinkerton, President Lincoln, and Major General John A. McClernand, Antietam, Maryland
Oct, 1862
Allan Pinkerton (1819 - 1884) created the Pinkerton National Detective Agency in 1850. He performed intelligence work for the Union during the Civil War. Photograph from the Battle of Antietam, September-October 1862. Library of Congress Prints and Photographs Division, LC-DIG-cwpb-04326.