The complete photo is at the Library of Congress Online, and is part of their Civil War Photograph collection.
TITLE/LABEL Unknown location. Modified 12-pdr. breech-loading Whitworth gun
PHOTOGRAPHER unknown.
CREATED/PUBLISHED Between 1860 and 1865.
MEDIUM 1 negative (2 plates) : glass, stereograph, wet collodion.
REPOSITORY Library of Congress Prints and Photographs Division Washington, D.C. 20540 USA
CALL NUMBER LC-B811- 3287
REPRODUCTION NUMBER LC-DIG-cwpb-02762 DLC (b&w copy scan of left half)
LC-DIG-cwpb-02761 DLC (b&w copy scan of right half)
LC-B8171-3287 DLC (b&w film copy neg.)
COLLECTION Selected Civil War photographs, 1861-1865 (Library of Congress)
DIGITAL ID (b&w copy scan of left half) cwpb 02762
http://hdl.loc.gov/loc.pnp/cwpb.02762
(b&w copy scan of right half) cwpb 02761
http://hdl.loc.gov/loc.pnp/cwpb.02761
(intermediary roll film) cwp 4a40638
NOTES Civil War photographs, 1861-1865 compiled by Hirst D. Milhollen and Donald H. Mugridge, Washington, D.C. Library of Congress, 1977. No. 0862.
Photographs of artillery, place and date unknown.