A police sergeant with an impeccable 26-year career record had one of the largest collections of child pornography in the UK.
Anthony King, 49, from Northolt, north west London, was jailed for 15 months at Southwark Crown Court after admitting 13 counts of making indecent images of children - some as young as five.
The court heard he had spent nearly £5,000 building up a collection of 25,000 pictures of children from all over the world obtained through the internet.
He was discovered after a US online porn distribution company was prosecuted and individuals were traced by the credit card numbers.
The FBI passed on the names of up to 3,000 UK citizens to Scotland Yard's paedophile unit.
Peter Zinner, prosecuting, told the court that King was in the process of destroying some of the evidence as he was arrested.
"This is one of the largest private collections that an individual has had," he said.
Sentencing him, Judge Gerald Gordon told King: "Save for one dark corner of your life, you are a man of the highest character with an impeccable record.
"However it is that dark corner which brings you before the court today - that is your active obsession with child pornography."
King's counsel Marion Smullen said he should be spared jail because he had instantly admitted his guilt and sought treatment for his obsession.
But Judge Gordon told King that if it were not for customers like him "there would not be worldwide porn makers".
He said sentences must deter others and "drive home the message that there are no sexual secrets on the net".
The 49-year-old will be put on the sexual offenders' register for 10 years and disqualified from working with children.