The term pareidolia is derived from the Greek words para, meaning something faulty, wrong, instead of, and the noun eidōlon, meaning image, form, or shape. Pareidolia is a type of apophenia, which is a more generalized term for seeing patterns in random data.

To get a better understanding of human vision, we contacted Dr. Jess Taubert, who was awarded the ARC Future Fellowship and is currently working at the University of Queensland, analyzing the aspects of social cognition that are grounded in visual recognition.

"A lot of our cortex is dedicated to processing visual input, particularly the things (objects and people) that we look at," she told Bored Panda. "When we focus on something, our brain builds a high-fidelity representation of that thing which includes information about all of its physical properties but also things like 'do we recognize that specific chair as the comfortable one from our office' or 'do we like that specific person.' Outside of where we are looking, which is called our periphery, is a different story. Despite how it feels, we don’t have a good sense of the objects and people in our periphery."

Dr. Taubert said that in order to understand why we see meaning where there is none, we need to know that "our perception of the world emerges from a confluence of computations in different parts of the brain, some of them are in the visual cortex (which receives visual input from the eyes) but there are other influences from the circuitry responsible for memory, attention, and motivation. And these regions all talk to each other to make decisions about what we are seeing in an iterative process."

"We likely experience pareidolia because when something in the environment has face-like features, these features automatically ping the visual cortex, which sends a signal that propagates throughout the brain to query what it thinks we are seeing. Although the visual cortex very quickly realizes it’s made a mistake, the rest of the brain likely makes the decision that, truth aside, the tree trunk or the cup of coffee does look a lot like a face."

One of the most popular examples of pareidolia is the Shroud of Turin, a cloth bearing the image of a man — which some believe to be Jesus — who appears to have suffered trauma consistent with crucifixion.

The negative image was first observed in 1898, on the reverse photographic plate of amateur photographer Secondo Pia, who was allowed to photograph it while it was being displayed in the Turin Cathedral.

Some visitors to St. Mary's in Rathkeale, Ireland, say a tree stump outside of the church resembles a silhouette of the Virgin Mary.

Others think that damage to the Pedra da Gávea, an enormous rock outside Rio de Janeiro, Brazil, created an impression of a human face.

Then there are the images taken in 1976 by the Viking 1 mission, which supposedly showed a face on Mars that could have been the remnants of an ancient civilization.

Some even find ways to profit off of pareidolia. Diane Duyser of Miami, for example, sold a 10-year-old grilled cheese sandwich, which she said bore the image of Jesus, for $28,000 on eBay in 2004.

A more unfortunate case occurred a few years later. A cinnamon bun bearing a likeness of Mother Teresa was first discovered at the Bongo Java Café in Belmont, Tennessee, but after being on display for about 10 years, it was stolen on Christmas day in 2007.

We have a number of theories as to the cause of this phenomenon. Some say pareidolia provides a psychological determination for many delusions that involve the senses—they believe pareidolia could be behind numerous sightings of UFOs, Elvis and the Loch Ness Monster, and the hearing of disturbing messages on records when they are played backward.

American cosmologist and author Carl Sagan believed that pareidolia was a survival tool. In his 1995 book, The Demon-Haunted World – Science as a Candle in the Dark, he argued that this ability to recognize faces from a distance or in poor visibility was an important survival technique. While this instinct enables humans to instantly judge whether an oncoming person is a friend or foe, Sagan highlighted that it could result in some misinterpretation of random images or patterns of light and shade as being faces.

Dr. Jess Taubert thinks that facial pareidolia is so evident because our brain has a strong sense of what a face is.

"From the moment we are born we orient towards faces and face-like patterns so, by the time we are fully grown, we have had a lot of practice detecting faces."

Leonardo da Vinci, on the other hand, thought pareidolia was an artistic device. "If you look at any walls spotted with various stains or with a mixture of different kinds of stones, if you are about to invent some scene you will be able to see in it a resemblance to various different landscapes adorned with mountains, rivers, rocks, trees, plains, wide valleys, and various groups of hills," he wrote in a passage in one of his extensive notebooks.

We have practical uses for pareidolia, too. Remember the Rorschach inkblot test? It is a projective psychological assessment developed in 1921 by Hermann Rorschach to measure thought disorders for the purpose of identifying mental illness. (It was inspired by the observation that schizophrenia patients often interpret the things they see in unusual ways.)