This primary source comes from the Records of the Office of the Chief Signal Officer.
National Archives Identifier:
524905Full Citation: Infantry regiment in camp. [Probably 96th Pennsylvania Infantry at Camp Northumberland near Washington, DC, ca. 1861] Mathew Brady Collection. (Army); ca. 1861; Mathew Brady Photographs of Civil War-Era Personalities and Scenes, 1921 - 1940; Records of the Office of the Chief Signal Officer, Record Group 111. [Online Version, https://www.docsteach.org/documents/document/infantry-regiment-in-camp-[probably-96th-pennsylvania-infantry-at-camp-northumberland-near-washington-dc-ca-1861]-mathew-brady-collection-army, April 26, 2024]