Magic Eye puzzles split society into two groups during the 1990s - those who could see the hidden images and those who couldn't.
These dot-filled pictures, known as autostereograms, produce a 3D image when the viewer arranges their eyes a certain way while looking at a 2D pattern.
And although Magic Eye puzzles were all the rage some 25 years ago, the idea has been used by scientists for decades to study depth perception.
Magic Eye puzzles are viewed at a "divergence distance equal to the width of one repeat of the 2D 'visible' pattern,'" explains the Magic Eye website.
"If you're good at diverging, you can diverge your eyes twice that distance.
"This will cause you to see multiple, distorted hidden objects in 3D."
Divergent viewing means, instead of looking directly at the image, you move your eyes as if you are looking right through it.
Stereograms were first used in the study of human depth perception, specifically how our eyes see different images and our brains create a single cohesive one - an autosterogram does not require a special machine to see the hidden 3D image.
Human pupils are usually 66 millimeters apart, which results in each eye seeing pictures slightly different.
The brain steps in during this process to create a complete picture so we aren't constantly experiencing double vision.
It is also the slight differences our eyes see while looking at the same picture that helps our brain create the best approximation, which is known as stereopsis - a term associated with the perception of depth and three-dimensional structures.
This idea dates back to the 1930s, where it was first described by the English inventor Charles Wheatstone.
He created a device that could display a slightly different image to each eye, in order to understand how our eyes take in images of 3D objects.
Using flat images, this was the first time scientists were able to trick the brain into perceiving depth - creating in the first stereoscope.
The next big breakthrough happened in 1959, when Dr. Bela Julesz was able to eliminate the depth cues of a photo, reports the Magic Eye website.
Julesz also discovered the first random dot stereogram while experimenting with stereopsis when he created one uniformed image that consisted of randomly distributed dots.
In the image, Julesz selected a circular area of dots within the image and slightly shifted the area in a second image, reports Mental Floss.
The random dots contained a hidden shape that could only be seen when you arranged your eyes at a certain point.
Anyone staring at the two images would see a floating circle, even though the random dots had no depth cues.
These findings supported Julesz's hypothesis that depth perception occurred in the brain and not in the eyes.
When you let your eyes diverge, instead of looking directly, for example, an icon, each eye is seeing its own icon.
Because your brain is trained to transform two similar pictures into one, it automatically assumes you are seeing one icon that is further back and larger - not two that are closer.
This happens across the entire image and every icon is being interpreted as one.
The right-most and left-most icons don't have pairs on their other side so you see end up seeing seven - five illusionary icons and the ones positioned on the edge.
"Pairs that are repeated at closer intervals, appear nearer to you, Vox explains in a video.
"So it's the interval of repetition that can be manipulated to adjust depth.
"And if we go from icons to something smaller you can start to see how they build a 3D image that can be easily camouflaged with noise".
Magic Eye puzzles begin with a 2D pattern that repeats itself, but there are also select dots, or pixels shifted to create depth and the 3D image.
Some 20 years after Julesz's discovery , Christopher Tyler, a student of Julesz, used computer programming to this offset scheme could be applied to a single image.This created the first black and white, single-image, random dot stereogram.
In 1991, Tom Baccei, an engineer, and Cheri Smith, a 3D artists teamed up to improve the researcher of Julesz and Tyler.
"No more dots! Using this new program in combination with state of the art 3D modeling software and colorful art techniques, a totally new patented art form was developed... Magic Eye," reads the Magic Eye website.
To create a Magic Eye image, programmers first start with the hidden image as a grayscale, smooth gradient depth map where dark points that should be furthest away are darker and closer points are in lighter shades, reports Mental Floss.
Then, the 2D pattern is placed over the hidden images as a camouflage.
And the computer will then use a Magic Eye algorithm that takes the image model and the pattern and arranges the repeating patterns to the necessary depth of the hidden image.
When someone looks at a Magic Eye, the repeating pattern feeds the brain the depth information encoded into it, and the brain perceives the hidden picture.