Not surprisingly, the Mona Lisa has come in for the closest scrutiny by nonexpert experts. Hidden images in the painting have been found by many. Ron Piccirillo, an artist in Rochester, New York, has claimed on his website that when he looked at the painting upside down and followed “the highlights of her portrait,” he was able to spot “what turned out to be a lion’s head, an ape head and a buffalo head.” He added that “for me, it helps to only use one eye,” and that the viewer should be “extremely close to the left edge of the painting.”

Silvano Vinceti, an art-history sleuth who runs something in Italy called the National Committee for the Promotion of Historical and Cultural Heritage, claims that he can discern minute letters painted in Mona Lisa’s eyes. In the right eye, for instance, he detects the letters L and V. The Louvre says that it has examined the painting with “every possible laboratory test” and has found no letters. This might have been a disappointment—the letters would have made Louis Vuitton a perfect corporate sponsor.

Claims about the background landscape in the Mona Lisa have become something of a growth industry. A paleontologist at the University of Florence, Carlo Starnazzi, argued in the mid-1990s that the lake on the left side of the painting is Lake Chiana and that the bridge on the right is the Burgiano Bridge, both near Arezzo. An art historian, Carla Glori, wrote in her 2010 book, The Leonardo Enigma, that the bridge in the painting can be found in Bobbio, a village south of Piacenza. An artist-photographer, Rosetta Borchia, and a geomorphologist from the University of Urbino, Olivia Nesci, believe the location is the Montefeltro region of northern Italy, and that the bridge can be seen from the heights of Valmarecchia.

In the eyes of some, the Mona Lisa raises medical issues and questions of physiological identity. Vito Franco, a professor of pathology at the University of Palermo, maintained in 2010 that Mona Lisa—the woman herself, Lisa Gherardini, the wife of Francesco del Giocondo, the Florentine silk merchant who commissioned Leonardo to paint the portrait—likely suffered from a cholesterol problem. Franco noted a yellowish accumulation of what he interpreted to be fatty acids under the skin. Kemp, at Oxford, checked the area under magnification and arrived at a different diagnosis: Residue from restoration efforts had “bleached.” One art historian, Angelo Paratico, in 2014 argued (in the same breath) that Mona Lisa might have been a Chinese slave and Leonardo’s mother.

Another theory: The Mona Lisa is a portrait of a man—either Leonardo himself or his pupil and possible lover, Salaì—dressed as a woman. The self-portrait theory found expression in a 1987 Art & Antiques article by Lillian Schwartz, an artist and computer technician who used digital tools to superimpose an image of a Leonardo self-portrait onto an image of the woman in the painting. No question, Schwartz concluded: Leonardo used himself as a model. A similar conclusion is reached in a video now on YouTube titled “Mona Lisa IS Leonardo da Vinci.” The viewer is urged to watch the overlay of a Leonardo self-portrait onto an image of the Mona Lisa in order to see “how amazingly they line up.” The notion that the Mona Lisa is a Leonardo self-portrait is not one that experts have rushed to embrace.