Gordon Simpson said his size had led to a poor self-image and he ended up spending a lot of time on the internet.
Simpson also tried to blame his brother and friends for the crime, but finally admitted responsibility.
The 26-year-old, from New Alyth in Perthshire, was ordered to carry out 100 hours unpaid work.
He was also placed on the sex offenders register and made the subject of a Sexual Offences Prevention Order (SOPO) for a period of five years.
The SOPO bans him from being alone with children, from having more than one phone and computer, and from using the internet before the police install monitoring equipment on his devices.
Solicitor Mike Tavendale, defending, told Perth Sheriff Court: “Because of his size his self-image is very poor and as a result of that he has become very socially isolated within the home.
“He spends most of his time, when he is not caring for his grandfather, on the internet. He is a first offender. He has never been in any form of trouble before.”
The court heard Simpson initially pointed the finger at his friends – despite them trying to protect him by not reporting what they had discovered by accident on his computer.
He then told the police that one of the computers containing the images was not his and could only have been used by his younger brother.
However, Simpson finally admitted to two charges relating to about 2,000 images, downloaded between 15 April 2011 and 21 November 2012.