Three of them showed girls between the age of 9 and 12 in sexualised poses. The others were three-dimensional computer-generated images showing "a close resemblance to real people", according to a summary of facts.
Court documents said they depicted male children being indecently assaulted by adult females.
Electronic analysis showed they were downloaded while Purvis admitted he had the laptop.
Police also found other images on the computer - children as young as 6 doing gymnastics and 8-year-olds posing in skimpy outfits. However, none was deemed objectionable by law.
On August 17, someone had used the laptop to visit three online chat websites targeted at children and teens. Analysts could not determine whether Purvis had communicated with anyone while online.
During sentencing, Judge Macdonald questioned probation as to whether there was any programme he could order Purvis to attend after he completed his sentence. But the defendant stood in the dock shaking his head.
"I've tried working with Department of Corrections psychologists. Problems were brought up and I have no trust in them," Purvis told the judge. Asked whether he would consider engaging his own therapist, he baulked at the idea of paying "$180 a session".
Purvis was jailed for 18 months.
Judge Macdonald refused to order counselling post-imprisonment if he was setting Purvis up to fail.
It is understood it will be at least his fourth prison term for such offences.
