Obscene images (which is open to interpretation, but currently mostly those showing explicit genitals) published in Japan need to be censored. That law is hundreds of years old and unlikely to be changed, because tradition.
Uncensored images can be
- made by someone who doesn't care about the law (though people have gone to jail for this)
- manually decensored
- made by someone who isn't in Japan (often Korea or Taiwan) and not posted on a Japanese website
- published outside of Japan (e.g. by Trimax or Fakku)