Scott Bowring, 40, of Dundee, was originally jailed for nine years for the offences, and ordered to be under supervision for a further three after admitting downloading and distributing images.
But judges at the Criminal Appeal Court in Edinburgh cut the jail term to eight years after ruling that he was not give enough of a reduction for his pleas over the child pornography crimes.
Bowring was caught with more than 77,000 still images and 5,000 video clips and it took nearly 17 days for police to work through his entire collection.
Sentencing him, Lord Tyre said: “You have in effect traded in this despicable material, regardless of whether any money changed hands.”
Defence counsel Moira MacKenzie said Bowring had sought help.