Police found a tranche of photos depicting child abuse and bestiality on Norman Lever's computer after raiding his home in Devon.
In one picture, they recognised an animal being abused as his mother's collie dog, Exeter Crown Court heard.
Lever, 31, was given a 12-month prison sentence, suspended for two years.
He admitted possession of extreme pornography and three counts of making indecent images of children.
Lever, of Bradwick Cottages, Kentisbury, near Combe Martin, was also ordered to attend a sex offenders course.
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Police raided his house on 15 January, 2015 and 274 child images were found on three computers, along with seven extreme images of bestiality.
They were able to prove the picture of him abusing his mother's dog was taken at his home by comparing the pattern on a carpet in the background.
Judge Geoffrey Mercer, QC, said: "I have to sentence you for the possession of photographs which to any right thinking person are quite repulsive. This is a serious offence.
"It is deserving of a prison sentence, but having read the probation report, I have no doubt whatsoever that the public interest is better served by you going on a sex offenders' programme."
The court heard that the dog was held in kennels for 20 days before being returned to Lever's mother.
Mr Richard Crabb, defending, said Lever's mother had given the police and animal welfare authorities assurances she would not leave the animal alone with her son again.
A man who photographed himself performing a sex act with his mother's dog was given away by a "prominent" tattoo on his hand, a court heard.