Another optical illusion is frustrating viewers and dividing internet opinion.

An image posted to Instagram by Swiss photographer Tiziana Vergari shows two girls reflected into mirrors making it as though there are dozens of girls in the frame.

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

A post shared by tiziana vergari iPhoneography (@tizzia) on

It was posted with the hashtag #whpidentity, as part of an Instagram Weekend Hashtag Project that aimed to celebrate identity.

Over 21,000 people have liked the post, with more than 4000 comments debating how many real people are present in the image.