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.
Mona Lisa
"Mona Lisa" has no clearly visible eyebrows or eyelashes. Some researchers claim that it was common at this time for genteel women to pluck these hairs, as they were considered unsightly. In 2007, French engineer Pascal Cotte announced that his ultra-high resolution scans of the painting provide evidence that "Mona Lisa" was originally painted with eyelashes and with visible eyebrows, but that these had gradually disappeared over time, perhaps as a result of overcleaning. Cotte discovered the painting had been reworked several times, with changes made to the size of the Mona Lisa's face and the direction of her gaze. He also found that in one layer the subject was depicted wearing numerous hairpins and a headdress adorned with pearls which was later scrubbed out and overpainted.