Doing a little more thinking on the nature of a situation like this.

you'd have to isolate the exact segment of data and perform whatever algorithms are needed to view it...in that way, let's say someone made an illegal representation out of lego blocks, then dismantled the representation, and kept the instructions for how to recreate said image, and then sold the kit of legos...by the logic our troll friend used, the recipient of said lego kit would be guilty of sharing illegal content, as the contents could be reconstructed into an illegal image  The end user does not posess the knowledge to recreate the content, and even if they did, it seems like this extra step of obfuscation would be incredibly useful in legal matters. (I don't even know how to y-enc etc etc).  Then again...I don't know shit.

edit* OR

A graffiti artist tags a wall with an illegal representation.  A security camera across the alley is pointed at the wall, and is subsequently transmitting said image.  Surely the users of the security system couldn't be targetted. etc etc