One picture in question, Kaplan told the high court in oral arguments, is "just a girl, not in an unnatural pose, standing on a beach."

But Assistant Attorney General Laura Dupaix argued that the photos Peterson downloaded were clearly intended for the "purpose of sexual arousal." They were not, she said, mere nudity.

"The statute covers content. That is what's prohibited," Dupaix told the justices.

It's that kind of thinking McCullough says he cannot understand.

"I think they seem to be trying really, really hard to say, 'If a person has a predisposition (to be aroused by something), he ought to to be locked up. We ought to find a way.' And I can't handle that," he said. "Good heavens, lots of things are innocent enough and can be misused, but you can't be responsible for everybody's thoughts."

But that's not what prosecutors set out to do, Dupaix said. For example, someone "turned on" by looking at children modeling underwear in a Sears catalog would not be prosecuted, she said, because the purpose of the catalog is clearly not sexual arousal.

Although there are several high-profile state cases right now, Montgomery said Utah law doesn't have as much bite as federal child pornography statutes. Under federal law, "if you are in possession of even one picture of a child engaging in a sexual position," you've got something, she said. Whenever possible, she said, task force members look to prosecute under federal statutes.

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"Would artificial images be as satisfying or arousing to them as the real thing?"

—Utah assistant attorney general Craig Barlow on virtual child pornography

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But even federal laws are tangled in legal debate. In January, the U.S. Supreme Court agreed to hear a case involving "virtual" child pornography — computer-generated images of children engaged in sex acts.

The case comes out of a lower court in California, where several representatives of the adult entertainment industry sued to stop the enforcement of the 1996 Child Pornography Prevention Act.

Through that law, Congress banned computer-altered pictures that only appear to show minors involved in sexual activity. Proponents say that by banning sexual images that do not actually portray children, the market for child pornography involving real children will lessen.

The 9th Circuit Court of Appeals found the law to be vague and overbroad.

Utah officials disagree about how a ruling on the case would affect the way they prosecute child pornography here.