Child porn fights and technical understanding of the internet

Fighting child porn on the internet has created many issues, mainly related to the adaptation of criminal law to the internet. A series of cases in the UK showed that interpretating the concept of posssession of obscene materials was not as straightforward as one could think. Often the problems arise from the lack of understanding of the technical aspects of the internet. In that sense, see the following story "Did You Know Caching Is How Perverts Avoid Downloading?" (TechDirt, 18 December 2008)

Note that reading or viewing can hardly be criminalised without infringing on free speech and without condemning innocent people. We sometimes come across porn unvoluntarily and see porn: to criminalise viewing would lead to criminalise anybody. Plus the difficulties to prove that the person actually viewed for a few seconds or for hours?