The photography app has more than 80 million users worldwide.

Instagram, the mobile photo-sharing service, has sparked fresh controversy after failing to ban images encouraging anorexia and self-harming.

Eating disorder support charity Beat has accused the Facebook-owned app, which has more than 80 million users worldwide, of "promoting anorexia" after it allowed users to view pictures of emaciated girls and super-skinny celebrities.

More extreme photos on the app contain messages encouraging people to starve themselves. Users are also given the option of 'liking' the images.

Although the social networking site is heavily moderated against harmful images such as pornography, users on the hunt for pro-anorexia images can find them by simply searching for hashtags such as #ana and #thinspo.

One image uploaded on the app, which is popular with teenage girls, includes the caption: "Go back to school skinny and shock everyone."

Another disturbing photo reads: "I like the feeling of being faint. The little two-second blackouts whenever I stand up. It shows that it's working."

Other images focus on self-harming and show users with cuts to their arms. One caption reads: "I have more scars than friends."

A Beat spokesman said: "It's worrying that with the powerful medium of social networking and the growing popularity of phone apps such as Instagram, people are able to easily access images that encourage the individual to believe that an eating disorder is a lifestyle choice and to avoid treatment.

"Some sites have acted to remove content that is seen as dangerous and encouraging people to do dangerous things. Eating disorders as a lifestyle choice should be treated in the same way.

"Beat also believes that individuals should be pointed towards pro-recovery sites - providing acceptance and support throughout society so that these alternative sites are no longer the only refuge a person feels they can seek."

Earlier this year Instagram updated its community guidelines and hinted that it planned to ban pro-anorexic content.

"[WE] Don't promote or glorify self-harm: While Instagram is a place where people can share their lives with others through photographs, any account found encouraging or urging users to embrace anorexia, bulimia, or other eating disorders; or to cut, harm themselves, or commit suicide will result in a disabled account without warning," the company said.

"We believe that communication regarding these behaviors in order to create awareness, come together for support and to facilitate recovery is important, but that Instagram is not the place for active promotion or glorification of self-harm."

The charity's concerns come days after Instagram provoked worldwide outrage when its new terms of service suggested user photos could be used in advertisements.