Over the past year, the Internet has served up its fair share of brain teasers with “ #TheDress” that broke the Internet, the cat going up or down a staircase, and now this “mind boggling” Instagram photo:

 

Same but different | My entry #whpidentity for @instagram [thank you #instagram for this featuring ❤️]

A photo posted by tiziana vergari iPhoneography (@tizzia) on

So, how many girls do you see in this picture? Two? Four? Five? Or 13?

Swiss photographer Tiziana Vergari uploaded the photo last week as part of an Instagram weekend hashtag project “#WHPidentity,” which encourages users to submit images that highlight individuality. While many people left comments of appreciation for the photo, one common question kept coming up — how many girls are actually in the photo?

The picture has generated over 15,000 likes and about 2,000 comments from people trying to decipher how many girls are in it.

If you look closely, the girls are sitting by mirrors. This is what creates an optical illusion, making it difficult, but not impossible, to tell how many girls are in the image. When we see visual stimuli, the eyes must focus light on its retina, convert the light into electrical impulses, and send those impulses to the brain in order to be interpreted, reports the National Eye Institute. When those electrical impulses arrive in the visual cortex of the brain, it reads them and translates them into an image of color and light. Then, it flips the image and fills in for the blind spot if needed. This all happens instantaneously.

Now, in the case of Vergari’s photo, the color, light, or pattern of the image can “trick” the brain into interpreting this image incorrectly. So, this can lead you to see something differently than the way it really is. This is called an optical illusion.

To put all theories to rest, Vergari revealed the most popular (and correct) one: there are only two girls, believed to be her daughters, in the photograph. One is looking in a mirror, one looking away, with that image repeated. The optical illusion is due to how the camera's positioned, not allowing the eye to see the mirror the closer sister is looking at.

Mirrorgate resolved.