I haven't yet heard of a case in the US where the only contention was that they had pictures of naked children on their computers. But of course the law could change, or police could get more aggressive in their definition of child pornography.
It's probably the case that many people have at least one image that can be viewed by someone as child pornography on their computer. Some of these may just be small pics that pop up when the user goes to a link they didn't intend or were tricked into clicking.
We're all guilty of something. If and when the government needs our compliance they will provide the evidence (real or faked up) to do their bidding or go to jail in disgrace.
>>But of course the law could change, or police could get more aggressive in their definition of child pornography.
Read the law for yourself, from the website of the Justice Department.
http://www.justice.gov/criminal/ceos/citizensguide/citizensguide_porn.html