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 replicas and reinterpretations
"Mona Lisa" is in the public domain and free to be exploited, explaining its reproduction on everything from postcards to coffee mugs, with no legal repercussions.
Artistic replicas and reinterpretations as a whole – demonstrating adequate modification – are considered "new" works eligible for copyright protection.
A fine example is artist Marcel Duchamp's "L.H.O.O.Q.", a 1919 work of art in which Duchamp embellished existing print-reproductions of Leonardo's "Mona Lisa" by merely adding a goatee ("shown below").
While copyright laws do not protect Leonardo's "Mona Lisa", Duchamp's "L.H.O.O.Q." falls within parameters of copyright law constituting "new" works.
For such reasons, "Mona Lisa" is commonly referenced academically in copyright courses.