Even that opens up a lot of troubling possibilities when you get computers involved. Does scrolling /b/ and having the thumbnail of a picture that turns out to be an actual rape in your cache count as "possession?" If I email a bunch of rape porn to David Cameron, is he in "possession" of it? What if he downloads the attachment before realizing what it is? Ridiculous, sure - but what if it's not him but a suspect for other crimes or a political nuisance?