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'Mona Lisa' - 'Mona Lisa,' painted by Leonardo da Vinci, is known for its hidden mysteries, such as the portrait's cryptic smile.

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'Mona Lisa' - Italian historian Silvano Vincenti claimed to have discovered secret symbols in Mona Lisa's eyes not visible to the naked eye, including the painter's initials "LV" in the right pupil.

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'Lady with an Ermine' - The original version of this famous painting did not include an ermine. Reflective light technology revealed that Leonardo da Vinci painted the animal later.

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'Isabella' - The Independent revealed that studies of this painting, by John Everett Millais, suggest the character in the foreground, dressed in white tights, is actually hiding an erection.

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'Boy Mozart' - Several theories regarding this painting by Pietro Antonio Lorenzoni indicate that it includes Masonic symbols. Mozart's hidden left hand may represent a hierarchical rank in the secret society.

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'The Garden of Earthly Delights' -

Hieronymus Bosch is beloved for his chaotic paintings, such as the epic 'Garden of Earthly Delights.' 

The main message can be seen in the egg, which is seen balanced on top of a horseman's head. This egg is painted in the direct center of the artwork.

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'The Garden of Earthly Delights' - It's theorized that, by using exterior panels, Bosch intended the artwork to be its own egg of sorts, one that is cracked and uncracked every time someone engages with the elaborate painting.

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'Girl with a Pearl Earring' -

'Girl with a Pearl Earring,' by Johannes Vermeer, is a painting that has mystified audiences for decades. However, what is that hanging from her ear?

Some argue that the girl isn't even wearing an earring. Look close, there isn't a loop that links the object to her ear. Many believe the painting to be an illusion.

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'The Prophet Zechariah' -

The celebrated painter Michelangelo created this work in the Sistine Chapel. He had a strained relationship with Pope Julius II, yet represented him in the figure of the biblical prophet Zechariah, together with two angels.

However, one of the angels is making a gesture known as "the fig," an obscene gesture, that has led many to speculate about its significance to Michelangelo and Pope Julius II's feud.

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'Netherlandish Proverbs' - Pieter Bruegel's work from 1559 illustrates various proverbs and is estimated to contain around 100 in total.

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'Nighthawks' - It is speculated that one of the most famous paintings of the 20th century, by Edward Hopper, doesn't actually depict a New York restaurant in Mulry Square, as originally believed. Instead, it's apparently an amalgamation of several spots in the city.

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'An Old Man in Military Costume' - This work was painted around 1630, by the famous Dutch artist Rembrandt van Rijn.

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'An Old Man in Military Costume' - Advanced imaging techniques have discovered a hidden, unfinished painting beneath the layers of oil paint.

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'The Life of Saint Francis' - This painting, located in the Basilica of Saint Francis of Assisi, and created by the Italian medieval artist Giotto, dates back to the 13th century.

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'The Life of Saint Francis' - After going unnoticed for centuries, it was discovered by medieval art expert, Chiara Frugoni, that the artist hid a smiling devil in the background of the painting, as reported by The Telegraph.

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'The Persistence of Memory' -

The melting clocks in this work, by surrealist painter Salvador Dalí, were inspired by images of melting Camembert cheese, as outlined by Mental Floss.

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'The Lute Player' - For a long time, the person in this Caravaggio painting was thought to be a woman. Only at the beginning of the 20th century did art critics realize that it depicts a young man playing a lute, an instrument considered masculine at the time.

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'The Birth of Venus' -

Crafted by Sandro Botticelli, 'The Birth of Venus' is an iconic Renaissance masterpiece from the mid-1480s.

Venus's golden hair is the focus here, as it curls around, creating a near mathematical curl that has since entranced viewers over the centuries.

In the 17th century, mathematician Jacob Bernoulli named the curl 'spira mirabilis,' which translates into 'marvelous spiral.' It's said the same curl is seen in sea shells and in the movement of birds.

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'The Creation of Adam' -

Some scholars point out that a human brain is hidden in the figure of God in this world famous painting by Michelangelo.

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'Broadway Boogie-Woogie' - The work was painted by the Dutch artist Piet Mondrian after he moved to New York City. The picture actually depicts the city grid of Manhattan.

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'The Starry Night' - Researchers came to the conclusion that Van Gogh was shockingly able to capture the concept of turbulent flow in this painting, which is one of the most difficult concepts in physics and mathematics.

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'Patch of Grass' - This 1887 painting is one of Van Gogh's most famous works, and depicts the colors of nature.

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'Patch of Grass' - In 2008, scientists from the Netherlands and Belgium used X-ray technology to discover a hidden portrait behind this painting.

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'The Ambassadors' - The strange object shown in the foreground of this painting, by Hans Holbein the Younger, is actually a human skull.

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'Supper at Emmaus' - This work was painted by Caravaggio in 1601, and shows Jesus revealing himself after his resurrection. The painting is full of religious symbols, including grapes that represent Christ's blood, and a pomegranate that represents his resurrection.

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'The Last Supper' -

Another painting that is thought to contain secret messages is Leonardo da Vinci's 'The Last Supper,' created in the 15th century. Certain elements of the painting were interpreted as corresponding to musical notes and forming a melody.

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'The Bayeux Tapestry' - 'The Bayeux Tapestry,' created in the 11th century, is more than just an iconic artwork. It's also a thrilling story of the Norman Conquest of England.

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'The Bayeux Tapestry' - The climax of this story is the killing of King Harold, who was seemingly shot in the eye with an arrow.

However, Harold is seen grabbing the arrow, which is said to be a metaphor for the reader's eyes, that have been pulled forward scene by scene.

See also: The most expensive paintings sold at auction

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