A teacher has admitted blackmailing teenage girls and demanding sexual images from them.
Zahid Akram, 37, entered guilty pleas to four charges of blackmail and one of causing or inciting a 13-year-old girl to take part in pornography.
Exeter Crown Court heard Akram, of Redditch in Worcestershire, used the internet to persuade girls to pose in their underwear.
Akram threatened to expose the images unless the girls provided pictures that went "certain steps further" and pay for mobile phone top ups, the court was told.
The father-of-two even messaged one terrified victim the Christian names of her parents and threatened to show them the pictures if she did not meet his demands.
Judge Francis Gilbert QC, The Recorder of Exeter, adjourned the case for pre-sentence reports but told Akram he faced prison for the "very nasty" offences, which took place in 2011 and 2012.
"These offences are very, very serious and they demand an immediate sentence of imprisonment," the judge said.
"This case involves blackmailing four young girls via the internet and in a very, very nasty way.
"He is a teacher, he is 37; he is an intelligent man. I regard these as very serious offences. He knew perfectly well what he was doing.
"What he was doing was extremely nasty.
"Getting young girls on the internet to take their clothes off and show themselves wearing their underwear and then - in the first girl's case, blackmailing her and writing her parents' Christian names to her - saying he will show the photographs unless they go certain steps further, putting appalling pressure on them."
At a previous hearing earlier this month, Akram admitted four charges of blackmail between September 16 2011 and January 11 2012.
The charges state Akram made "unwarranted demands" for sexual images and money in the form of phone credit "with menaces".
He also entered a guilty plea to a charge of causing or inciting a child to take part in pornography between November 25 and November 30 2011.
Akram, who resigned from his teaching post on August 30 last year and said to be in £40,000 of debt, was ordered to register as a sex offender.
Sean Brunton, prosecuting, did not open the case at today's short hearing.
Lawrence Wilcox, representing Akram, asked for the case to be adjourned so reports could be carried out.
He said: "Through the references so far, it is obvious that he has depression. It appears from what he reports he has a number of physical ailments.
"He lost a brother at an early age, his mother has dementia, his father is in poor health. His financial difficulties are acute."
Mr Wilcox said Akram, who wore a smart suit and carried a large bag into court, was a man of previous good character and has two young daughters.
The case was adjourned until next month and Akram was remanded in custody.
Dr Richard Steward, headteacher of Woodroffe School in Lyme Regis in Dorset, said in a statement: "In the autumn of 2011, the school was contacted by the police regarding an investigation into the activities of a member of staff, Mr Akram, who was working here as a physics teacher at the time.
"Following the initial phone call, Mr Akram was immediately suspended from his duties and sent home, pending further investigation.
"Mr Akram did not return to school and resigned his post during the course of the investigation.
"The school worked closely both with the police and Dorset safeguarding officers throughout.
"The school has been assured by the police that none of the offences which led to Mr Akram's arrest have any connection with the school or the local community.
"The school's internal procedures have confirmed this and we are confident that Woodroffe students were completely safe during the period that Mr Akram was employed here.
"The school has moved on and continues to maintain exceptionally high standards with regard to child protection and student safety."