▲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.

▲Advanced imaging techniques have discovered a hidden, unfinished painting beneath the layers of oil paint.

▲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.

▲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.

▲The original version of the famous painting did not include an ermine; reflective light technology revealed that Leonardo da Vinci painted the animal in later.

▲This work was painted in 1630-1631 by the famous Dutch artist Rembrandt van Rijn.

▲The Independent reveals that studies of this painting by John Everett Millais suggest the character in the foreground dressed in white tights is actually hiding an erection.

▲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.

▲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.

▲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.

▲This famous 15th-century painting by Italian artist Domenico Ghirlandaio has been at the center of debates for many years. Alien theorists believe that there is a UFO painted in the sky in the background.

▲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, but is instead an amalgamation of several spots in the city.

▲Some scholars point out that a human brain is dissimulated in the figure of God in this fresco painting by Michelangelo.

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

▲The work of Mona Lisa, painted by the famous Leonardo da Vinci, is known for its hidden mysteries, such as the portrait's cryptic smile.

▲This 1887 painting is one of Van Gogh's most famous works and depicts the colors of nature.

▲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.

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

▲

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.

▲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.

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

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

▲This work was painted by Caravaggio in 1601 and depicts 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.

▲

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

▲

This work was created by painter Hieronymus Bosch between 1490 and 1510. It's a triptych which includes three paintings on separate panels, each depicting common themes within Christianity.

Many have speculated about the hidden symbols in this great piece of art, but art historian Hans Belting was the first to theorize that the artist included a self portrait in the painting, although it cannot be verified.

▲

To create this painting, abstract expressionist artist Jackson Pollock placed the blank canvas on the floor and used towels, knives, and wooden sticks to apply the paint.

▲

Many works of art hide mysteries and secrets that we are not aware of at first glance. Behind the canvases of great artists, such as Leonardo da Vinci, Van Gogh, or Pablo Picasso are subliminal messages, hidden secrets, and details that you never knew were there.

Uncover the greatest secrets hidden in classic works of art in the following gallery!