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It seems simple enough, how many girls are in this image?

Yet people are freaking out online as they argue about the number of people actually in the shot.

As with the infamous dress, this Instagram post has taken a life of its own becoming a viral sensation with over 17,400 likes since it was uploaded last week.

We have Swiss photographer Tiziana Vergari (@tizzia) to thank for this latest head-scratching viral snap. She originally posted the image as a contribution to Instagram’s weekend hashtag project, a series where the platform sets a weekly challenge for users around a theme.

Last week’s topic, #WHPidentity, asked the Instagram community to share images and video “celebrating individuality.”

But, the ‘optical illusion’ of seeing a row of the same faces repeated has caused confusion.

It seems no one can agree. Is it 13? Or 3? Or 2 sets of twins? Or something else entirely?

One user left baffled by the snap resorts to focusing on the little details posting: “Four, two of the girls have bracelets on plus the eye line is different on two of the girls.”

But using that same logic, another says: “I see 6 girls when you look at the bracelets.”

Vergari, meanwhile, has confirmed that the photograph she took features — drum roll please — two sisters looking into a mirror.

Despite this, users continue to debate the number of girls and how the “optical illusion” was captured in the first place.

Looks like this one will continue to attract thousands of comments as the debate rages on.