And what's the difference between porn and hentai?
The difference is with Porn, you have to take the good in with the bad. If they have a blemish or scar or whatever, you see it. Hentai is art in its purest form: a drawing, which is made to typically unrealistic porportions with no flaws or blemishes. Porn has real women who are being photographed, and as such, are as is. A drawing can be modified to look almost any way you want it to be.
The problem with hentai is that it portrays unrealistic images of men and women, and therefore can make the viewer feel imperfect themselves.
They're both a form of sexual art, though.