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.
Mona Lisa (Prado's version)
After the restoration, it was suggested that two of Leonardo's pupils, Francesco Melzi or Salaì, were among the probable painters, though others questioned this assumption; they suggest the author could have been a Spanish student of Leonardo, namely Fernando Yáñez de la Almedina or Hernando de los Llanos. The painting cannot be considered as a typical workshop copy due to its careful and thorough execution, as well as its use of materials such as lapis lazuli or red lacquer.