From the Flemish painter Cornelius Gijsbrechts, a painting of the back of a painting (1670):

“The Reverse of a Framed Painting was not intended to be hung on the wall, but to be placed against it,” writes Olaf Koerster. “The viewer would be deceived into trying to turn the picture around, only to see the reverse of an unframed painting: Gijsbrechts had created the paradoxical painting with two backs.”