The mind-boggling image has gone viral since it was posted on Instagram by Swiss photographer Tiziana Vergari last week.
The picture features what appears to be a group of girls sitting by some mirrors.
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This creates an optical illusion, making it difficult to tell exactly how many girls are in the photo.
The optical illusion has been shared thousands of times as internet users debate how many girls appear in the photo.
Thousands of social media users have posted comments giving their guesses, which range from two to 14 girls.
People have argued that a series of mirrors makes it seem that there are more people in the picture than there actually are.
The photo, which has been liked 14,400 times, was originally posted by Ms Vergari as part of an Instagram weekend hashtag project.
The photographer posted the photo with a caption reading: “Same but different”, leading many social media users to conclude there are two sets of twins in the image.
One Instagram user said: “4 girls. 2 sets of twins. Clue is in the description.”
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Another wrote: “There’s clearly four. Look at how the reflections are. If you see their face, the mirror shows the back of their head. If you see the back of the head, the mirror shows the face. The girls just look similar.”
Ms Vergari confirmed there are actually only two girls in the photo, who are believed to be her daughters.