Well, it’s a sepia-toned photographic negative image of an 1875 painting by George Augustus Holmes titled “Can’t You Talk?”
It might be an ‘ambrotype’ negative where the captured image on a glass plate, when viewed by reflected light against a black background, appears to be a positive image. Ambrotypes first appeared in the 1850s and went out of fashion with the appearance of ‘tintypes’ in the 1860s. There have however been a number of successors to the process, including some rather more recent ones generically referred to as ‘reverse printing onto glass’. It would take some very close examination to determine exactly what process has been used here and how old it might be.
Addition: Holmes' painting was heavily reproduced as prints, so the image is more likely to have been taken from one of the prints.