That last post from Killjoy got me thinking. So here is a quick run down of Who will have a Litigation fit for pic packs. Anyone should feel free to add more since this is definitely not a comprehensive list.
With the exception of Linda Project, I don't think I have ever heard of a Japanese artist or Circle suing or even asking for the removal of there artwork from a NA site. As a matter of fact, there is a general feeling of "There gonna steal it anyway so why bother" And "I can't be bothered with another language" amongst the JP art community. So using images from those artists isn't gonna get people in trouble.
There are also sources from hentai foundry, random artist sites as well as a few pay sites here in North America | Europe. Amongst these, Hentai key is the only one who bitches about there IP. (Zone doesn't seem to care though.) Jiggle Girls is surprisingly mum on the subject. And everyone else seems to so far ignore there images ending up on sites like rule 34, e-hentai or danbooru.
As far as real porn star or actress images are concerned, I'm not really sure. For Porn stars, I think as long as it's part of there preview set, they don't care. (Stuff you can find on freeones.com). For actresses however, you are dealing with whatever news agency is taking the pictures. Though, with so many of these images ending up on blogs, I really don't see how they can start suing people now.