Many Japanese paysites use stolen content from Japan-based domestic AV-idol sites.
http://www.graphis.ne.jp
This is the original source that idolbucks and many others have an eye on. They just crop the watermark at original pictures then make their own FHGs and members content.
Proof:
the original picture
cropped picture Idolbucks using
http://www.idols69.net/pictures/689-Yui-Seto/index.html