A County Tyrone man is at the centre of "one of the most serious cases of sexual exploitation of children" the National Crime Agency has ever had to tackle, one of its officers has said.
Michael Dynes, 38, from Rossin View in Dungannon, allegedly targeted young people through advertisements seeking life models on the Gumtree website.
He would then "audition" them by webcam and try to incite them into committing sexual acts, a court was told.
He is facing a series of sex charges.
They include making and possessing indecent images of children, having what are described as extreme images and committing an act outraging public decency.
He is also accused of engaging in sexual acts in the presence of children and inciting children to watch another person engaging in sexual acts.
Mr Dynes was arrested as part of the first joint operation between the National Crime Agency (NCA) and the Police Service of Northern Ireland, known as Operation Jarra.
His home was searched at the start of June.
The charges relate to various dates between 2009 and this year.
Mr Dynes appeared in Dungannon Magistrates' Court as the charges were read out.
He had been on bail since June while a forensic examination of what was found in his home took place.
That report revealed that his computers contained hundreds of images, the court heard.
Other extreme material was also recovered.
An NCA officer in court opposed bail and said the investigation had revealed Mr Dynes was chatting with boys and girls online and trying to incite them into committing sexual acts.
The judge refused bail and Mr Dynes will appear again by video-link next month.