This is a faithful photographic reproduction of an original two-dimensional work of art. The work of art itself is in the public domain for the following reason:
In many jurisdictions, faithful reproductions of two-dimensional public domain works of art are not copyrightable. The Wikimedia Foundation's position is that these works are not copyrightable in the United States (see Commons:Reuse of PD-Art photographs). In these jurisdictions, this work is actually in the public domain and the requirements of the digital reproduction's license are not compulsory.
