A former Canberra music teacher, caught in a global police operation, did not realise anyone was being hurt by his obsession with child pornography, a court has been told.

The man downloaded nearly 15,000 images including graphic videos of girls, as young as five, being gagged and raped by men, and children performing sexual acts with other children and having sex with animals.

Richard Llewelyn, 58, from Chisholm in Canberra's south, has pleaded guilty to one charge of possessing child pornography and one charge of using a carriage service to access the material.

Llewelyn was arrested and forced to resign from his teaching job in March after police discovered the images on two home computers and 61 DVDs.

His arrest was part of a worldwide investigation into child pornography called Operation Centurion.

Llewelyn developed an interest in the material after he found out his father had molested his own children, a sentencing hearing of ACT Supreme court was told today.

He soon became obsessed with the internet and accessed the material every night for sexual gratification.

His obsession became so extreme that he suffered deep vein thrombosis because of the time spent on the computer in 2005.

Llewelyn claimed he did not realise anyone was being hurt by the images when he was accessing them, a statement of facts read out by commonwealth prosecutor Jon White said.

Mr White said Llewelyn, who has been diagnosed with Attention Deficit Disorder and vertigo, had sought psychiatric help for his condition.

Since then he had shown "deep remorse" and was "horrified" at the realisation the children in the images had been victims.

"He (Llewelyn) is deeply ashamed of his offence," Mr White said.

The court was also told that Llewelyn's wife and three grown children were supporting him.

They have described him as "a very kind person who would not hurt anyone".

The hearing has been adjourned until September 26.