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.
Speculations about Mona Lisa
German imaging researchers Claus-Christian Carbon of the University of Bamberg and Vera Hesslinger of the University of Mainz performed further analysis of the Museo del Prado version, comparing it to Da Vinci's "Mona Lisa", and in May 2014 speculated that, based on perspective analysis of key features in the images, the two images were painted at the same time from slightly different viewpoints. They further proposed that two images may therefore form a stereoscopic pair, creating the illusion of 3-dimensional depth, when viewed side by side. However, a study published in 2017 has demonstrated that this stereoscopic pair in fact gives no reliable stereoscopic depth.