There are several photographs that were taken, about mid-1864, of the Confederate POWs (as well as civilian detainees) of Fort Warren. One of the most fascinating of these photos is a group of officers of the Confederate States Navy, in a group, with other prisoners, taken at the front of the facility. The Naval Historical Foundation has a copy of this image, though its quality is not as good as another copy of the same photo, available from a New York resource. See the link shown below for a copy of this latter image, as well as details of the persons shown in the photo.