Optical illusion developed by Edgar Rubin, 1915

Gates of palace of Sargon II at Khorsabad, 721-705 BCE

Performance installation by Marina Abramovic and Ulay, 1977

Terracotta sarcophagus, 520 BCE

Sculpture by Jeff Koons, 1990

Sculpture by Gian Lorenzo Bernini, 1621-1622

Photograph by wired.com, Drpoulette, Creative Commons

Photograph by huff_photos

Photograph from John Stabley, 2008

Photograph from the making of a film by Leni Riefenstahl, 1936

Photograph by Sylvietsak

Detail from fresco painting by Giotto, c. 1303-1310

Photo from Getty Images/AFP, 2008

Photograph from Smithsonian Institution National Anthropological Archives

Sculpture probably by Master Heinrich of Constance, c. 1310

Photograph of heads for film by Lucio Fulci, 1980

Detail from fresco by Luca Signorelli, 1499-1502

Photograph from Radio Free Europe, 2006

Engraving by Pieter van der Heyden, 1557

Still from film by Michael Powell, 1960