London: A portrait auctioned by Christie's for a little more than USD 21,000 may be a priceless piece of art by Leonardo da Vinci, art experts have claimed.
They believe that the mystery painting, which appeared in 1998, seems to have come from a 500-year-old book containing the family history of the Duke of Milan
It could be the portrait of the duke's daughter made by da Vinci for her wedding book, said art historian Martin Kemp, of the University of Oxford.
"We knew it came from a book, you have the stitch holes and can see the knife cut. Finding it is a miracle in a way. I was amazed," Kemp said. "When doing historical research on 500-year-old objects... you hardly get the circle completed in this way."
In 2010, Kemp first suggested that da Vinci painted the portrait, and since then, art historians have debated over both its origin and the painter.    

An earlier examination of the artwork by a gallery in Vienna led the director there to say it was not a da Vinci, and they are unswayed by the new evidence.
The portrait was sent to Christie's in 1998, with art historians there suggesting the piece came from 19th-century German artists called the Nazarenes, who mimicked the Renaissance style.
But, this was disproved after carbon dating estimated the creation of the portrait, titled 'Head of a Young Girl in Profile to the Left in Renaissance Dress', could be between 1440 and 1650.
Kemp wasn't convinced and started looking into the painting's history. He first saw the portrait as an attachment to an email in 2008, and immediately recognised da Vinci's left-handed style.
Da Vinci was an artist in the duke's residence between 1481 and 1499. He was the only left-handed artist in the court at that time, the researcher said. Kemp then went to see it in Zurich and his co-researcher Pascal Cotte, engineer and founder of art analysis start-up
Lumiere Technology, examined it in Paris.
Kemp and Cotte then published "La Bella Principessa: The Story of the New Masterpiece by Leonardo da Vinci", claiming the work might be a da Vinci.
The portrait is made on vellum, a specially prepared skin normally used for writing and printing. No work by da Vinci has been found on vellum before, though it was frequently used in books.
Many believe the portrait came from a book, because three stitch holes are visible on the portrait's left margin. It is also made of chalks and ink, not paint.
"It was apparent from the evidence we got about the vellum and the missing sheets, within reasonable margins of doubt, that's where it comes from," Kemp said. "At 500 years old, you never have as much confirmation as you like, but this is as good as it gets."
Kemp and Cotte have published a short version of their examination of the book and the portrait's cut marks and binding, along with their analysis of the vellum online. The painting has been renamed "La Bella Principessa," though its true origins are still debated.