How many girls are really here: two or four?

How many girls are there in this photo? The question has sparked a widespread debate among social media users since the “mind boggling” photograph was posted to Instagram last week.

Swiss photographer Tiziana Vergari originally posted the photo online as part of an Instagram weekend hashtag project. Labeled #WHPidentity, the project encourages users to submit photos that showcase individuality.

But the photo, which has been liked more than 16,300 times, has become something of an optical illusion when people started debating how many girls were posing in the photo.

The picture features a group of girls sitting by some mirrors, creating an optical illusion that makes it nearly impossible to tell how many girls are in the image.

Some claimed identical twins could be seen, some say there are only four girls and others 13.

The photographer cleared things up, saying she only has two daughters.This probably indicates that the girls in the photo are her daughters. But that didn’t stop thousands from enjoying the internet puzzle.

Join the puzzle solving on Instagram: Tizia

*Storification by Xinhua