One in four women deliberately put unflattering photographs of friends wearing bikinis on social networking websites such as Facebook, according to a study.

The majority of women posting the photos said they did so after falling out with their friends, and nearly a third said they were taking revenge on people who had done the same to them.

Two-fifths of women admitted posting photographs of their friends without make-up. Even when asked to permanently delete the unflattering picture from Facebook, a fifth of women said they had refused to do so.

The survey of 1500 women aged over 18 by, a photo gift website, adds to growing evidence that people use Facebook to embarass or humiliate their friends.