Yellow butterfly. ca. 1890. Oil and graphite. Collection of the Yale University Art Gallery, New Haven. Image Courtesy of the Yale University Art Gallery. In the public domain in the United States because it was published before January 1, 1924. via https://commons.wikimedia.org/wiki/File:Yellow_Butterfly_by_Albert_Bierstadt.jpeg
“Sunset, Tropical Marshes, Florida.” ca. 1880. Oil on canvas. Martin Johnson Heade, artist (1819-1904). Collection of the Morse Museum. In the public domain in the United States because the artist has been dead over 70 years. via http://www.morsemuseum.org/collection-highlights/paintings/heade-painting