From the GWV website: "Classical and Renaissance art is represented in the museum's rare collection of 48 plaster casts. In Victorian America's art museums, casts provided what was for most visitors the only contact with ancient sculpture. The casts in the G.W.V. Smith Art Museum are remarkably accurate reproductions of these masterpieces, made from molds taken directly from the originals."
This is actually a mirror. It's reflecting the painting below.