License, verbatimPD
The National Gallery of Art: open access image with no usage restrictions under the NGA's open access policy (openaccess=1 in the Gallery's published_images dataset).
Adrian Zingg. A Landscape with a Herd of Cows and Goats, Surmounted by Another Landscape, Upside-down, with a Man Pushing a Wheelbarrow, c. 1800. National Gallery of Art, Washington.