Ex-JPL conceptual artist Kurt Wenner created this anamorphic drawing in 2010 for Greenpeace, to commemorate a million-signature petition opposing genetically modified crops in Europe.

Seen from this angle the illusion is so compelling that it’s hard to tell what’s what. Within the circle Wenner (addressing reporters) is real, as are the five people behind him bearing signs, and the bales immediately surrounding them. But I believe everything else within the ring is drawn. For comparison here’s an image by Pyramid Visuals, which produced the substrate on which the image was printed.

At 22 meters square, the image set a world record at the time as the largest of its kind drawn by a single person.

Simon Beck creates large-scale artworks by walking through fields of snow. Working primarily in the Alps, he creates about 30 drawings each winter, shuffling through pristine snowfalls guided by a compass. A single image can require 10 hours’ time and 30 miles of of walking.

“Making these drawings is map-making in reverse,” he told the Guardian. “You start with the map, and you need to make the ground agree with the map.”

Another reversible face, this one by British artist Rex Whistler (1905–1944).

The approach to Macon, Georgia’s 2012 International Cherry Blossom Festival was much safer than it appeared.

Artist Tracy Lee Stum’s anamorphic sidewalk painting took two days to create.

A reversible etching by John Kay, 1790.

From the National Portrait Gallery, London.

Francesco Queirolo’s 1754 sculpture Release From Deception depicts an angel releasing a fisherman from a net.

Unbelievably, the entire piece was carved from a single block of marble.

Historian Giangiuseppe Origlia called it “the last and most trying test to which sculpture in marble can aspire.”

See The Veiled Virgin and Folds of Stone.

After several delusional episodes, seamstress Agnes Richter was institutionalized at the University of Heidelberg Psychiatric Clinic in 1893, at age 49. While performing the needlework expected of female patients, she sewed a diary of sorts into a remarkable jacket pieced together of wool and linen. “Writing” in a now-obsolete German script, she recorded brief, enigmatic expressions reflecting life in a psychiatric hospital: I wish to read, I am not big, I plunge headlong into disaster. Her laundry number, 583, appears several times, apparently to ensure that the jacket was not lost during cleaning.

Another patient, Mary Lieb, institutionalized periodically at Heidelberg for mania, would sometimes decorate the floors of various rooms with patterns of cloth strips. The warders found some of these remarkable enough to photograph (below). Physician Hans Prinzhorn included some of the photographs in his collection of the art of the insane, and the images have survived to the present day as strangely vivid marks of an inscrutable self-expression.

“The patterns are extraordinary, comprising rows of starbursts (or perhaps flowers), letters, crosses, geometric patterns, and sometimes intricate curved figures,” writes Lyle Rexer in How to Look at Outsider Art. “Their purpose and organization are unclear, but like much outsider art, the work appears to be a combination of decoration and communication, an attempt to reorder the space ‘from the ground up,’ visually transform it, and invest it with new significance.” What it means only Lieb knew.