Posted By:
ramramI too originally made a fast assumption that it was a tintype (with the glass taped over the front). Later, when I looked again, it did appear to be an ambro with a piece of blackened tin behind. There also appears to be the remnants of a scalloped shape on the front of the glass which would be evident of it having been in a case at one time. That would also lend evidence to the image being from the early 1860's or sooner.
Rob M.