Mona Lisa replicas and reinterpretations
After restoration, the Prado's "Mona Lisa" revealed details covered by previous restorations and layers of varnish.
Furnishings and fabrics were enhanced, as well as landscape and facial features.
It is anticipated that such revelations may offer further insight into Leonardo's original.
Experts at the Louvre reportedly supported the Prado museum's findings.
The Prado replica was subsequently transported to the Louvre in 2012 to be displayed next to "Mona Lisa" as part of a temporary exhibition.
Two nude paintings bearing similarities to Leonardo da Vinci's original were part of a 2009 exhibition of artwork inspired by "Mona Lisa".
Displayed at the Museo Ideale in Leonardo's hometown of Vinci, near Florence, some believe one of the paintings – dating from Leonardo's time – to be the work of Leonardo himself, and it has at times been credited to him.
Other experts theorize the painting, one of at least six known to exist, may be just another copy painted by "followers" of Leonardo.
Scholarly dispute persists as to artist, subject and origin.
The nude in question, discovered behind a wall in a private library, reportedly belonged to an uncle of Napoleon Bonaparte, who owned another of Leonardo's paintings.
Facial features bear only vague resemblance, but landscape, compositional and technical details correspond to those of the "Mona Lisa" known worldwide today.
Speculations about Mona Lisa
One long-standing mystery of the painting is why "Mona Lisa" features very faint eyebrows and apparently does not have any eyelashes. In October 2007, Pascal Cotte, a French engineer and inventor, says he discovered with a high-definition camera that Leonardo da Vinci originally did paint eyebrows and eyelashes. Creating an ultra-high resolution close-up that magnified "Mona Lisa"s face 24 times, Cotte says he found a single brushstroke of a single hair above the left eye. "One day I say, if I can find only one hair, only one hair of the eyebrow, I will have definitively the proof that originally Leonardo da Vinci had painted eyelash and eyebrow," said Cotte. The engineer claims that other eyebrow hairs that potentially could have appeared on the painting may have faded or been inadvertently erased by a poor attempt to clean the painting. In addition, Cotte says his work uncovered proof that her hands were originally painted in a slightly different position than in the final portrait.