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).
Abraham Swan (author). Designs in Carpentry Containing Domes, Trussed Roofs, Flooring, Trussing of Beams, Angle-Brackets and Cornices, published 1759. National Gallery of Art, Washington.