Isleworth Mona Lisa
According to Leonardo's early biographer Giorgio Vasari, Leonardo had started to paint "Mona Lisa" in 1503, but "left it unfinished". However, a fully finished painting of a "certain Florentine lady" surfaced again in 1517, shortly before Leonardo's death and in his private possession. The latter painting almost certainly is the one that now hangs in the Louvre. Based on this contradiction, supporters of the authenticity of the "Isleworth Mona Lisa" claim it is the unfinished "Mona Lisa", made at least partially by Leonardo, and the Louvre "Mona Lisa" a later version of it, made by Leonardo for his own use.
Louis Béroud
Louis Béroud (January 17, 1852, Lyon-October 9, 1930, Paris) was a French painter of the late 19th, early 20th century. Some of his paintings are visible at the Musée Carnavalet and The Louvre in Paris. On August 22, 1911, Béroud came to The Louvre to sketch his painting "" but where the famous "La Joconde", by Leonardo da Vinci, should have stood, he found four iron pegs. Béroud contacted the section head of the guards, who thought the painting was being photographed for marketing purposes. A few hours later, Béroud checked back with the section head of the museum, and it was confirmed that the "Mona Lisa" was not with the photographers. The Louvre was closed for an entire week to aid in investigation of the theft.