It's debatable and I can’t find a web link that absolutely 100% nails it down, but I'd have to say that the image of Jesus Christ has been reproduced far and above anything else. They have been turning them out for over 2,000 years!
The average Boston College student is apt to recognize Edvard Munch’s work, if not the twentieth century Norwegian expressionist. Munch’s most famous work, “The Scream,” popularized on posters, mouse pads and mugs, has become the most often reproduced image in the world, with Leonardo DaVinci’s “Mona Lisa” following in second place.
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Guerrillero Heroico," Alberto Korda’s 1960 photograph of Che Guevara, is claimed to be the most widely reproduced image in the history of photography. The portrait has remained remarkably durable as a symbol of revolution and youthful rebellion, even as it has been endlessly reproduced on posters, t-shirts, and mass-produced objects. Examining the extraordinary power of this image and the history of its circulation, "Che! Revolution and Commerce" will be on view at the International Center of Photography (1133 Avenue of the Americas at 43rd Street) from December 9, 2005 through February 26, 2006.
http://www.telegraph.co.uk/culture/3675212/Che-Guevara-Revolutionary-and-Icon.html
Mickey Mouse’s image is the most reproduced in the world. Over 7,500 items bear his likeness. Jesus is number two, and Elvis is number three.
http://inventors.about.com/library/inventors/blkidprimer6_12toys.htm?terms=lincoln+logs