A PAEDOPHILE who used a picture of Justin Bieber on his internet chatroom page to groom hundreds of girls around the world has been jailed for 14 years.

Behind the photograph of the teenage pop heartthrob was balding pervert Robert Hunter, 35, whose crimes were described as "appalling" by sickened investigators.

Hunter - branded "every parent's worst nightmare" - was told by a judge that the case was the worst type of online abuse he had ever encountered.

Tonight, a source close to the investigation said: "It is terrifying to think what someone can persuade girls to do just by using a picture like that.

"He is every parent's worst nightmare. In a very calculated and chilling way, has wormed his way into the lives of these girls. What he did was appalling."

Teesside Crown Court heard how he used a video of a naked teenage lad masturbating - claiming it was him - to persuade the youngsters to do similar things for him.

Although ten girls appear on the charge-sheet, Hunter had made online contact with hundreds of others in the Far East, Europe, the US, Australia and in this country.

When his victims had second thoughts about doing what he instructed, he threatened to tell their relatives what they had been up to, prosecutor Richard Bennett said.

The loner also threatened to abduct one who stopped complying with his demands, and vowed to murder the brother of another who refused to do as he said.

His sickening collection of home-made sex films involving girls as young as nine was found after one of his victims alerted police thousands of miles away.

Officers in Tasmania were able to trace the paedophile through his sleazy computer use, and tipped off colleagues in the UK who raided his home in Middlesbrough.

The extent and depravity of his online activities is said to have shocked the most experienced detectives, who tonight welcomed the lengthy sentence.

After police raided his home in December 2011, they found a folder on his computer called "me" where he had created false identities such as Justin, Josh and Joshua.

Mr Bennett told Judge Peter Bowers that Hunter used a picture of 19-year-old Canadian superstar Bieber on his social networking site to disguise his true identity.

He contacted girls all over the world through Facebook, MSN messenger and a music site, and encouraged them to film themselves in sexual acts so he could watch on a webcam.

More than 800 films and stills taken from the online chats were discovered on his computer. None of the images he had amassed had been downloaded from the internet.

"Using a number of online aliases, he pretended to a number of very young girls that he was a teenager," said Mr Bennett.

"On each occasion he was able to disguise his true age and identity by the clever use of images of young boys.

"As a further demonstration of the naivety and innocence of his victims, he was also able to persuade some that he was the music artist Justin Bieber.

"He did this in order to dupe and encourage these young girls to strip on webcams and perform sex acts for him."

Hunter, of Brough Court, Middlesbrough, pleaded guilty to 15 charges of causing or inciting a child to engage in sexual activity and 14 of making indecent photos of children.

Judge Peter Bowers accused Hunter of "gross exploitation" and told him: "The deceits you used were elaborate, persistent and clever at times.

"It represents callous - almost sadistic - exploitation of young girls. Their feelings were manipulated and their naivety and vulnerability were undermined and used by you for your own benefit and personal gratification.

"This is one of the most serious cases of internet abuse the courts have dealt with in this area.

"It is certainly a salutary warning to all parents of teenage children and what is capable of being done on the internet and how it can be abused."

Miss Pawson said: "He knows what he did was wrong and knows that he needs punishment."

Judge Bowers added: "I am sure the public will be very disgusted by the way you behaved.

"If necessary, you were blackmailing them and for a young child that must have been a terrifying experience.

"They dare not confide in their parents and dare not confide in adults, and as a result, the threat of exposing embarrassing pictures of them on the internet was quite a real and frightening reality for them."

Detective Sergeant Paul Higgins said after the case: "Robert Hunter was a calculating and malicious predator who set out to coerce and bully young girls into exposing themselves over the internet.

"This investigation highlights the dangers that children face when conversing with people over the internet."