LONDON – OCTOBER 10: A visitor to the Pop Art Portraits exhibition at National Portrait Gallery looks at Andy Warhol’s ‘Marilyn Monroe (Marilyn) 1967’ on October 10, 2007 in London. 52 key works by 28 American and British artists are gathered together in the first exhibition entirely devoted to portraits by pop artists. The exhibition runs from October 11, 2007 to January 20, 2008. (Photo by Peter Macdiarmid/Getty Images)