Paul Leighton, 32, from Seaham, County Durham, created up to 40 fake Facebook profiles to befriend teenagers in the UK, Canada, the US and Australia.
He tricked them into sending him naked selfies, then blackmailed them into abusing young relatives.
He had earlier admitted a total of 21 offences at Newcastle Crown Court.
The court heard one 14-year-old from Florida was tricked into believing he was talking to a girl, then blackmailed into repeatedly raping his one-year-old niece.
