What would happen if you had 'real' child porn, but put it through a 'line drawing, edge detection and colour fill' shader on somthing like Photoshop or an auto Rotoscope'r video process.
Would it still count ? Could you tell it was from an original ?
Where is the line ? I can only see that actual acts against a real child can be sure to cross the line.
ps. I'm not advocateing downloading CP, just don't know how the law makers can say where then line is if image possesion alone is a criminal offense.