"The self-portrait was found on the back of Van Gogh's 'Head of a Peasant Woman' when experts at the Edinburgh gallery took an X-ray of the canvas ahead of an upcoming exhibition ... Van Gogh was known for turning canvases around and painting on the other side to save money." https://apnews.com/article/hidden-van-gogh-self-portrait-b703b4391c4ec0ba5bcf381ae44a6c3b