A visitor examines Andy Warhol's Marilyn

A visitor examines Andy Warhol's Marilyn Monroe 'Marilyn 1967' at the Pop Art Portraits exhibition, National Portrait Gallery in central London, 11 October 2007. The exhibition brings together 52 key works from one of the world's most popular and influential art movements -- Pop Art. 'Pop Art Portraits' contains works from 28 artists from Britain and the United States, including Andy Warhol, Roy Lichtenstein and David Hockney, and is designed to show how the genre evolved and revolutionised portrait painting. It examines how the artists depicted the famous and their use of images drawn from advertising, pop music, the cinema, magazines and newspapers. (Photo credit should read BEN STENSALL/AFP via Getty Images)