A mum pretended to be her 13-year-old daughter to catch a paedophile who had sent vile Instagram messages.
Nicholas Jackson, 46, was arrested at work and later jailed for three years after the parent tricked him into sending her his mobile phone number.
The woman was able to use the number to find Jackson's Facebook account and reveal his identity.
Leeds Crown Court heard on Friday the teenager's mum became concerned for her safety in October last year after reading messages on her Instagram page from an account called “Loose Hill Nick”.
Michael Collins, prosecuting, told the court the defendant had sent the girl messages describing her as "fit" and had asked "how far she would go."
Her mother then replied to Jackson pretending to be her daughter and discussed meeting him in Wakefield.
Jackson sent his mobile number and a message asking her to delete their conversation.
Mr Collins said the woman was then able to use the number to find Jackson on Facebook.
Jackson had his iPhone seized when he was arrested which was later found to contain over 1,000 indecent images of children.
A total of 436 images were at category A - the most serious level of offending.
Some images featured children as young a two being sexually abused.
Jackson, from Wakefield, pleaded guilty to three offences of making an indecent image of a child and three offences of breach of a sexual harm prevention order.
The defendant had been made the subject of the sexual harm prevention order in 2016 when he was convicted of making indecent images of children.
He also had previous convictions for drugs offences, criminal damage and breaching court orders.
Christopher Morton, mitigating, said Jackson was an internationally-renowned mountaineer and rock climber and he had committed the offences when he was suffering from depression and anxiety.
Jailing Jackson for three years and four months, Judge Rodney Jameson QC said: “They are not victimless crimes.
“Real children are raped in order to produce material of this type.”
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