This is an example of an anamorphic painting, a composition that can only be viewed with a special mirror that restores the deformed image. The painting is unrecognisable until a cylindrical mirror is placed at the centre of one edge. Examined from above, a butterfly at rest will suddenly come into view. Paintings of this type were popular during the 18th century, especially anamorphic portraits that concealed the identity of the sitter from prying eyes.
© Science Museum / Science & Society Picture Library