![[President Abraham Lincoln, Major General John A. McClernand (right), and E. J. Allen (Allan Pinkerton, left), Chief of the Secret Service of the United States, at Secret Service Department, Headquarters Army of the Potomac, near Antietam, Maryland]](https://images.metmuseum.org/CRDImages/ph/web-large/DP285633.jpg)
[President Abraham Lincoln, Major General John A. McClernand (right), and E. J. Allen (Allan Pinkerton, left), Chief of the Secret Service of the United States, at Secret Service Department, Headquarters Army of the Potomac, near Antietam, Maryland]
Alexander Gardner · October 4, 1862
Albumen silver print from glass negative