London (CNN) -- It is 100 years since Leonardo da Vinci's "Mona Lisa" was stolen from the Louvre Museum in Paris by an Italian handyman and secreted away for two years before eventually coming to light again.
While the world's most famous painting was thankfully retrieved, there remains a handful of missing works by the great master whose whereabouts are still the subject of feverish speculation.
The number of Leonardo da Vinci's paintings is small, "no more than 20," according to Martin Kemp, Emeritus Research Professor in the History of Art at Oxford University and a leading expert on Leonardo da Vinci.
But the re-discovery, this year, of a Leonardo painting named "Salvator Mundi" gives art lovers everywhere hope, said art crimes expert Noah Charney, author of "The Theft of the Mona Lisa" and founder of think tank, the Association for Research into Crimes against Art.
CNN takes a look at the famous lost works of Leonardo, and how likely it is they will ever be found again.
Charney and Kemp agree that the story of Leonardo's "Medusa Shield," which is detailed in art historian Giorgio Vasari's 1550 tome "Lives of the most eminent painters, sculptors and architects," may well be apocryphal.
But it remains a source of intrigue.
Vasari describes a young Leonardo painting onto a wooden shield the face of classical monster Medusa. The shield was later referenced in a painting by Caravaggio.
"If that shield exists, it would be a great trophy," Charney said.
"The Medusa Shield was meant to be one of these origin stories from Leonardo's youth, so it could be in Vinci (in Tuscany, where Leonardo was born), or it could be in Florence but these things tend to move around, especially if people didn't know it was a Leonardo, it might have entered a collection under a different name," he continued.
Kemp said that the survival rate of such an object is likely to be low, though similar painted shields from the period have survived.
But, he said: "It's not the sort of thing that would have been treasured from moment one as a great masterpiece."
It was to be the biggest bronze sculpture ever made in a single casting. Leonardo was to create a five meter-high bronze statue of a horse in honor of Milan's ruling family, the Sforzas.
He worked for 12 years on the project, and created a clay model of the horse, which was displayed in 1493, but was shot to bits when the French army invaded the city.
Charney believes that fragments of the model could still be out there.
"The French admired Leonardo as well," he said. "It wouldn't have been completely shattered if it had been used for target practice for archers so a portion of that could still exist, certainly," he continued.
There were also, according to Kemp, smaller models, as well as the outer molds of the clay horse.
"But they, again, are the sort of things that wouldn't survive (over time), you wouldn't cherish great, gallumping clay molds of horses for 500 years," he said.
'Battle of Anghiari'
In 1503, Leonardo was commissioned to paint a mural of a historical battle scene in Florence's Palazzo Vecchio.
It remained unfinished and has not been seen since the room in which it was partially painted was remodeled by Vasari around the mid-16th century.
Yet, some art historians believe it is still in the Palazzo Vecchio and that Vasari created a false wall in front of the mural to preserve it, not least because in one of his paintings in the Palazzo Vecchio are written the words: "Seek and you shall find."
"That one I'm quite sure is there, it's just a matter of time and also trying to figure out the logistics of having to sort it out yet -- of how you remove the Vasari fresco, which is a national treasure, without destroying it before you get to the Leonardo," said Charney.
A forensic expert in Renaissance art and architecture named Maurizio Seracini is currently trying to get the funding to locate the painting behind Vasari's. "It would be sensational if it appears and I wish Maurizio every success," said Kemp, though he added that if the unfinished painting has indeed been secreted behind a wall for 500 years, it would be in very bad shape.
The "imponderables," as Kemp calls them, include paintings for which copies and preparatory sketches exist, though no extant original works.
These include a picture of the Virgin with the holy children playing and one of St. John and Christ as children.
The "Salvator Mundi," which is incontestably authentic, according to Kemp, and which will be going on display in London's National Gallery in November, was one such work.
There are also lost notebooks; only around a fifth of Leonardo's notebooks and manuscripts, according to Kemp, have survived though a pair of bound manuscripts came to light in the 1966 in Spain, so it is not out of the question that more could appear.
Still, Kemp stresses that people should not get their hopes up for finding drawings and even less so for paintings.
"If you took a very optimistic view, you wouldn't get up to more than 30 paintings," he said.
The odds are stacked against these being found, he said, but that won't stop people trying -- such is the power of the legacy of the man from Vinci.