Whoa. Thanks to these answers on Quora for the inspiration.
1. Which one of these faces is female, and which is male?
Surprise: They’re actually the same androgynous face, just with different levels of contrast, which makes one appear male and one female. Read more here.
2. Stare at the cross. What’s wrong with these celebrities’ faces?
3. The Leaning Tower illusion
The two images of the Leaning Tower of Pisa are identical, yet one has the impression that the tower on the right leans more, as if photographed from a different angle.
Read more here.
5. Stare at this video for 45 seconds, then look at your palm.
6. Notice anything unusual about this photo of a parrot?
It’s not a parrot! It’s a woman covered in very meticulous body paint by artist Johannes Stoetter. See how he did it here.
7. Watch this spinning dancer for awhile. Is she spinning clockwise or counterclockwise? Does she change direction?
The illusion derives from the lack of visual cues for depth. Read more here.
8. This floor is completely flat.
9. Stare at the black cross for 10 seconds and see what happens.
The purple dots disappear! When one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point will fade away and disappear.
10. These monsters are the exact same size.
11. The squares marked A and B are the same shade of gray.
12. Is this photo in black and white, or color?
13. What’s happening here?
14. The spirals that appear blue and green are actually the same color.
The reason why we are perceiving one color as two different colors is because of the other colors surrounding the stripes.
Each eye has six to seven million cones, which are concentrated in a central yellow spot known as the macula. These cones measure color in different wavelengths, where some of which overlap. Our brain then compares by measuring the differences in wavelengths between the colors. When certain colors are combined, the brain can’t process the data from the cones correctly and we get confused.
15. Stare at the colored dots on the girl’s nose in the photo above for 30 seconds. Then look at a white surface and start blinking.
16. These two blocks are the same color.
Skeptical? Put your index finger over the line where the two boxes meet.
17. Try to focus on one of the dots.
If you keep your eyes on the black dots, they appear to form and vanish at the intersections of the horizonal and vertical lines. The effect is diminished if one is very close to the screen, further away or if one views at a 45 degree angle. This illusion is known as the Scintillating grid.
18. Try to focus on these spirals.
19. World’s Largest Lightness Illusion
In this illusion, it appears that there is one set of black figures and one set of white figures. In fact, the two sets of figures are exactly identical and the same color.
They appear different because the surrounding regions they are on cause the visual system to segment the images into layers. Thus one set appears to be white figures behind dark clouds, and the other set appears to be dark figures behind light clouds. If you cut out the figures, you’d see they’re identical.
20. The two orange circles are exactly the same size.
The one on the left seems smaller. This is known as the Ebbinghaus Illusion.
21. Stare at the yellow dots for awhile, and they’ll disappear.
22. How many legs does this elephant have?
23. Great photo of some cars on a street?