The seemingly bizarre tintype shown above is an example of a nineteenth-century image created using the "hidden mother" technique, explained at Accidental Mysteries:
You see, most infants during that time were photographed with their mothers holding them. The intended picture was ultimately headed for a frame or mat, so the child would sit in the mothers lap for the photo. When the picture was taken, the mother simply was cropped out to serve as the backdrop.
Additional examples may be seen at links here and here, and in this Flickr group pool.