I believe this image was taken at Drewry's Bluff in April 1865. The quarters in the background really look like those at Fort Darling and the gun is a banded Brooke Rifle which I believe were only at Fort Darling, Battery Brooke and Battery Dantzler. I don't think this image was taken at Brooke or Dantzler since to the best of my knowledge there were no regular wood frame quarters built there and if there were, they were not that close. Below is a photo of possibly the same gun taken at Drewry's Bluff from the rear. What appears to be the tompion is laying in the embrasure just like in the image you posted.