I don't know. But generally I think that you should link to the page containing the picture instead of to the picture directly.
Unfortunately on some agency sites, both individual photos and galleries will go out of date after a while and you'll end up with dead links in the threads. It's a problem we're just having to live with at TRF, but it beats "remove all our photos within seven days or you and your members will be hearing from our legal department."
If what you are getting at is you want to upload the pictures here so that they stay available, then I am quite certain that is illegal.
Yep. As long as they're being posted without permission, at any rate, and permission is expensive.
If you upload the pictures to some other picturesite and link to them, then i can't see any problem with that.
There's no problem as far as this forum is concerned, but the hosting sites themselves have rules about uploading copyrighted material. Not that anybody pays attention to those rules or anything, but they're still there. If an RD member posts a link to a copyrighted photo they've stored at Photobucket, they might be in trouble with the agency as a Photobucket member but not as an RD member. If they post a link to a copyrighted photo that someone else has stored at Photobucket, they haven't done anything illegal (as far as I know). Not that I'm giving legal advice here, but this is how I understand it from when we were updating our rules at TRF, and our owner had a lawyer involved in writing the Terms of Service that the rules are based on and in answering questions while we were writing the copyright rules.