It must have been apparent to everyone with a modicum of nous that Bill Henson's photos of nude teenage girls are not pornography by today's standards.
What appears to have happened is that he got caught up in a national crackdown on child pornography, in Australia. The latest news over here is that 90 people in a variety of professions (including one policeman) have just been arrested by the Federal Police for possession of child pornography and another 80 are under investigation. Another 40 arrests are planned for the near future and a few people have already committed suicide.