In recent years, art history scholars have unveiled Templar knights, Mary Magdalene, a child and a musical script hidden in the Italian's paintings.
It is well-documented that Leonardo, who lived between 1452 and 1519, often wrote in mirror writing, either in an attempt to stop his rivals stealing his ideas or in a bid to hide his scientific theories, often deemed as subversive, from the powerful Roman Catholic Church.
|These images, from the group's website, show how the original The Virgin and Child sketch (left) can be manipulated with mirrors to supposedly show the ancient Old Testament god Jahveh (right)
But now a group known as The Mirror of the Sacred Scriptures and Paintings World Foundation believes that he applied the same technique to some of his best-known creations, including the Mona Lisa and the Last Supper, to conceal mysterious faces and religious symbols.
When applied to the sketch The Virgin and Child with Saint Anne and Saint John the Baptist, which hangs in London's National Gallery, the authors say the mirror image reveals the ancient Old Testament god Jahveh, who "protects the soul of the body's vices" and wears the Vatican's crown.
Their theory would explain why many of Leonardo's characters seem to be pointing or staring into space, as if searching for the Divine.
The group claims they are indicating where the mirror should be placed to reveal the painting's secrets.
|The Mona Lisa supposedly shows a similar face
In the Virgin and Child sketch, they say, it explains why John the Baptist appears to be staring past Jesus into the distance.
A similar face appears when a mirror is applied to the right hand shoulder of Mona Lisa, and the experts also claim to have found an upturned holy grail on the table in front of Christ in the celebrated Last Supper fresco.
The mirror-technique is applied to another painting of John the Baptist to reveal the four-legged image of creation and the Tree of Life in Adam and Eve's Garden of Eden.
Again, John is pointing with both hands to the place where the mirror needs to be placed to reveal the "hidden" image.
According to the group, the same technique was used by Michelangelo and Raphael, in artwork exhibited in the Vatican, and Renaissance artists including the neoclassicist Jacques Louis David. Similar images have also been found in famous paintings and sculptures of Buddha.
The study's authors wrote to the Vatican last year to explain their discovery, but received a lofty reply saying that while their findings would no doubt be the object of much discussion in the art history world, their ideas required "solid proof" and needed to be supported by a general consensus among art critics before they could be taken seriously.
Critics of the project will claim the authors want to cash in on the worldwide fascination with Leonardo conspiracy theories, brought to a head by the publication of Dan Brown's Da Vinci Code and the subsequent Tom Hanks film.
These featured the theory that the male figure on Christ's immediate right is actually Mary Magdalene and the couple had descendants living in the modern world, and multiplied visits to sites all over the world to which Leonardo was linked.
The latest theory, expounded by The Mirror of the Sacred Scriptures and Paintings group, whose website www.mirrorandart.com, is owned by the Sacred and Divine Reason and Foundation Corp, follows the revelation in July by an Italian amateur scholar that the Last Supper contained a hidden image of a woman holding a child.
The figure, he said, appeared when the fresco was superimposed with its mirror image and both were made partially transparent.