Any good work of art deserves a closer look, but the illusions in these masterpieces really reward the viewer who makes a thorough inspection.

1. “The Ambassadors,” Hans Holbein the Younger, 1553

This sumptuous dual portrait of Jean de Dintevill and Georges de Selve emphasizes their wealth and worldly knowledge. The top shelf and bottom shelf contain objects representing the celestial sphere and the terrestrial sphere, respectively. Also on the bottom shelf is a lute with a broken string, a common symbol of strife. Given the particulars of the painting, here it is thought to specifically reference the discord brewing as Henry VIII prepares to break from the church.

The painting’s most obvious feature is a distorted image in the foreground that breaks sharply with the striking realism of the painting. The elongated blob is revealed to be a skull, but only when the painting is viewed from a certain angle, a technique known as anamorphosis. The skull is a common, unambiguous symbol of death and mortality but the illusionary rendering imbues it with a little more nuance — the skull can only be seen when the rest of the painting is obscured, and vice versa.

2. The Secret Portrait of Bonnie Prince Charlie, 1700s

In the case of “The Ambassadors,” the anamorphosis was employed as an artistic flourish within an otherwise conventional painting. But the technique could be used to obscure an entire image. Such is the case with this “secrete” portrait of Charles Edward Stuart, a Jacobite pretender to the English throne. After a rousing defeat at the Battle of Culloden, the Jacobite cause was effectively eliminated and to support Stuart’s claim to the kingdom was considered treason. Those still loyal to Charles, however, could continue to raise a glass in his honor with this tray. When a reflective glass was placed in the middle, the meaningless blur would reveal a portrait of Bonnie Prince Charlie.

3. “Eye Scream Sunday,” Aakash Nihalani

Street art is increasingly recognized and respected as a medium, and Aakash Nihalani has found an untapped niche with his use of neon tape to create bold geometric shapes that challenge the viewer’s sense of perspective. The illusions created are relatively simple, the same way you can draw a cube that looks three-dimensional, but his work takes advantage of the cityscape and, in his latest series, even city-dwellers.

4. “Gala Contemplating the Mediterranean Sea Which at Twenty Meters Becomes the Portrait of Abraham Lincoln (Homage to Rothko)”, Salvador Dali, 1976

Of course you can’t talk about illusions in art without talking about Salvador Dali, whose surrealist paintings played on a number of optical illusions. In this painting, Dali is exploiting a specific feature of how the human mind processes images. Dali had read a Scientific American article about the number of pixels necessary to identify a human face. In response, he created this work which, when viewed from close up seems to portray Gala watching the Mediterranean sun, but when viewed from twenty meters away is a portrait of Abraham Lincoln composed of 121 distinct “pixels”.

5. “Enchanted Beach With Three Fluid Graces,” Salvador Dali 1938

The “Graces” here appear to be an amalgamation of the Greek Graces, beauty, charm and joy, and the Three Fates, who control the life thread of every person. In Dali’s depiction of them, the figures are seamlessly woven into their surroundings, with features that appear humanoid from a distance but are actually comprised of entirely separate objects upon closer inspection. Facial features are formed from rocks or horses or even other people. The most ethereal of the Fates on the far left actually appears to be part of a skull, if you look at it just right.

6. Andrea Pozzo's dome at Sant'Ignazio, 1691–1694

The dome, apse, and ceiling of this Jesuit church in Rome feature some of the most incredible examples of di sotto in sù (“seen from below”) and quadratura, techniques developed during the Italian Renaissance that employ different theories of artistic perspective to give flat ceilings the appearance of grandiose depth. The fresco presents not only an artistic masterpiece but a visual illusion that the church is more opulent than it really is as well. One particular stretch shows an elaborate scene of heavenly splendor that appears to spring out of the architecture itself.

7. “Escaping Criticism,” Pere Borrell del Caso, 1874

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Di sotto in sù and quadrature are themselves examples of trompe l'oeil (“deceive the eye”), a technique that utilizes forced perspective and hyper-realism to depict objects that appear convincingly three-dimensional. This painting of a boy seemingly climbing out of the frame is just one of many examples from the era.

8. “Bâtiment,” Leandro Erlich," 2012

This art installation in the heart of Paris made it seem like acrobatic pedestrians were dangling from the façade of a four-story building. Erlich created this effect by painting a building exterior, complete with three-dimensional windowsills, on the ground and then reflecting the life-sized image into a giant upright mirror.

9. 3D Chalk Art, Julian Beever

One of the modern masters of trompe l'oeil, Beever paints sidewalk murals that appear to have remarkable depth. With remarkable realism and deft shadowing, he makes the flat surface appear to be the teetering edge of a tall building or a tranquil reflective lake. Because of the forced perspective, all of his drawings only work from one vantage point. When viewed from any other angle, they appear incredibly distorted.

10. Surrealist photographs, Thomas Barbéy

If you think illusions can’t exist in photographs, think again. Barbéy’s images juxtapose radically unrelated photos to create surrealist works of art that make it look as though a piano’s keys grow out of a zebra’s stripes or mountain peaks crest into horse heads.

11. “Evolving Picture” and others, Oleg Shuplyak

Almost all of the oil paintings by Ukrainian Shuplyak employ a similar technique to Dali’s “Enchanted Beach…” Portraits of historical figures are hidden in lush landscapes. The faces of John Lennon, Pablo Picasso, Sigmund Freud and Charles Darwin are rendered in varying degrees of obviousness by smaller figures or related paraphernalia.