An internet cartoon showing characters modelled on Bart, Lisa and Maggie Simpson engaging in sex acts, is child pornography, a judge has ruled in a landmark case.

In February at Sydney's Parramatta Local Court, Alan John McEwan was convicted of possessing child pornography and using his computer to access such material.

He was fined $3,000 and required to enter a two-year good behaviour bond in relation to each offence.

McEwan appealed against the conviction, but it was dismissed in the NSW Supreme Court, with Justice Michael Adams concluding a fictional cartoon character is a "person" within the meaning of Commonwealth and NSW laws.

"The alleged pornography comprised a series of cartoons depicting figures modelled on members of the television animated series The Simpson," the judge said.

"Sexual acts are depicted as being performed, in particular, by the "children" of the family.

"The male figures have genitalia which is evidently human, as do the mother and the girl."

He noted the figures made no pretence of imitating any actual, or fictional human beings.

"In particular, the hands bear only four digits and the faces have eyes, a nose and mouth markedly and deliberately different to those of any possible human being," he said.

The magistrate had rejected a submission that cartoon depictions or representations of fictional characters such as The Simpsons were not of "persons".

Justice Adams said the legislation's main purpose was to combat the direct sexual exploitation and abuse of children that occurs where offensive images of real children are made.

But, he said, it was also calculated to deter production of other material, including cartoons, which "can fuel demand for material that does involve the abuse of children".

He upheld the magistrate's conclusion that the figures in the cartoons were depictions of persons within the meaning of the definitions in the laws.

Justice Adams ordered each party to pay its own costs, as it was the first case dealing with the "difficult" issue.

-AAP