More than half of the selfies clicked are about appearance of people, highlighting their make-up, clothes and lips, according to a study that analysed 2.5 million pictures on popular photo-sharing website Instagram.

Researchers from Georgia Institute of Technology in the US combed through selfie posts on website Instagram to determine what kinds of identity statements people make by taking selfies.

They gathered the data by searching for hashtag '#selfie,' on the popular picture sharing website and then used computer vision to confirm that the pictures actually included faces.

Researchers found nearly 52 per cent of all selfies fell into the appearance category: pictures of people showing off their make-up, clothes, lips, etc.

Pictures about looks were two times more popular than the other 14 categories combined.

After appearances, social selfies with friends, loved ones and pets were the most common (14 per cent). Then came ethnicity pics (13 per cent), travel (seven per cent), and health and fitness (five per cent).

Researchers noted that the prevalence of ethnicity selfies (selfies about a person's ethnicity, nationality or country of origin) is an indication that people are proud of their backgrounds.

They also found that most selfies are solo pictures, rather than taken with a group.

Researchers noted that overall, an overwhelming 57 per cent of selfies on Instagram were posted by the 18-35-year-old crowd.

The under-18 age group posted about 30 per cent of selfies. The older crowd (35+) shared them far less frequently (13 per cent). Appearance was most popular among all age groups, researchers said.

Selfies are an identity performance – meaning that users carefully craft the way they appear online and that selfies are an extension of that.

“People project an identity that promotes their wealth, health and physical attractiveness. With selfies, we decide how to present ourselves to the audience, and the audience decides how it perceives you,” said Julia Deeb-Swihart from Georgia Institute of Technology.

“Selfies, in a sense, are the blending of our online and offline selves. It is a way to prove what is true in your life, or at least what you want people to believe is true,” Deeb-Swihart said.