|The Ambassadors by Hans Holbein the Younger.|
The Ambassadors, by Hans Holbein the Younger, was painted in 1533. In addition to being a double portraiture, it is famed for the long greyish mark twisted slantwise across the bottom of the picture, which, viewed at an acute angle from the edge of the frame, appears as a human skull seen in perspective.
A reference to this or similar paintings can be found in Shakespeare's play Richard II, in which the character Bushy uses it as a simile:
For sorrow's eye, glazed with blinding tears,
Divides one thing entire to many objects,
Like perspectives, which rightly gazed upon
Show nothing but confusion; eyed awry