Potter Stewart once said he couldn't define it but   knew it when he saw it (I'm not sure if he was speaking from experinece or merely being glib.) In any event as the article says the supreme court defined "obscene" in Miller  to mean: a work taken as a whole that  lacks artistic merit, depicts certain conduct in a patently offensive manner and violates contemporary community standards. That means pornography does not necessarily have to involve minors to be illegal.

The grant, about $150,000 a year, has helped pay for Mr. [Tom] Rogers and another retired law enforcement officer in Reno, Nev., to harvest and review complaints about obscene matter on the Internet that citizens register on the Justice Department Web site.

Speaking of Reno, this page does a good revisit of Reno:

Listen, people in this field have an enormous apetite for porn. But this decision today, by the Ninth Circuit will most likely ultimately lead to faster normalization, as they feed their appetites for ever more naked totty, (under "pretext of law - color of authority", of course):

"To the extent our cases have predicated the reasonableness of an airport screening search upon either ongoing consent or irrevocable implied consent, they are overruled." (In a fifteen-judge en banc panel decision by the Ninth Circuit today)

That is because these airport, see-through-the-clothes scanners (still in their infancy, they will soon get far better detail), are in the pipeline and will be an especially big hit for examining kids.

Now consider how the government impinges upon adults by §2257, with a flimsy argument of expediency, (after Niccolo Machiavelli - doctrine of expediency; theory that the end justifies the means, irrespective of how unscrupulous or Draconian such actions may be.)