Mystery surrounds the identity of the "Mona Lisa," with some people positing that the smiling figure is in fact a self-portrait of Leonardo da Vinci himself, while others believe it was a coded portrait of a male associate.
Giotto's fesco of the ascension of St. Francis in the Basilica of St. Francis in Assisi.
A devil's face was recently discovered in the swirling cloud at the center of the fresco.
A detail of the devil's face discovered in the fresco.
Michelangelo's "Last Judgement" at the Sistine Chapel in the Vatican is believed by some to contain coded messages preaching religious tolerance.
Caravaggio's painting, "The Supper at Emmaus," contains subtle clues pointing to the true identity of the beardless man at the head of the table.
An Italian musician believes that the positioning of the disciples' hands and the bread rolls on the table could be read as musical notes, suggesting a secret requiem threaded into the work.