From the public domain images of artworks in the Metropolitan Museum of Art collection -
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Title: Chief Officer and Clerks of the Ambulance Department, 9th Army Corps, in Front of Petersburg, Virginia
Artist: Timothy H. O'Sullivan (American, born Ireland, 1840-1882)
Printer: Alexander Gardner (American, Glasgow, Scotland 1821-1882 Washington, D.C.)
Date: August 1864
Medium: Albumen silver print from glass negative