A nationwide child pornography ring was unearthed after a paedophile left his phone on a Tyneside bus, police said.
Michael Fraser's mobile was found to contain images of child pornography when it was discovered in Newcastle last year.
Officers used information on the 50-year-old's handset to track down other suspected paedophiles in what police described as an ongoing operation.
Fraser has been sentenced to a three-year community order.
He admitted a string of offences relating to the possession of indecent images of children, at Newcastle Crown Court on Wednesday.
The details of the porn ring emerged after Fraser left his mobile on a bus travelling between Newcastle's Metrocentre and the city last February.
The phone was handed to police after it was found to contain the indecent images.
Officers searched Fraser's home where they found more phones containing indecent images of children.
Fraser, who now lives in County Durham, was ordered to sign on the sex offenders register for five years.
Among those already jailed as part of the investigation, known as Operation Cammell, is paedophile David Walton from the Gateshead area.
The 48-year-old was given an indeterminate jail sentence last year for the possession and distribution of a number of indecent images of children.
Northumbria police would not confirm the total number of people arrested as part of the investigation, as the operation is still ongoing.
But Det Chief Insp Paul Young, said: "This investigation started with the finding of a mobile phone on a bus.
"It led to numerous arrests and the recovery of a number of other phones - several of which contained indecent images of children.
"There have been a number of arrests in relation to the operation across the country and investigations are still ongoing."