The to-do with the website that was linked to here and which, apparently, had something illegal on it... there's a way to save yourself stress in such cases.
First, engage in nothing illegal, of course.
Second, if you see something obviously illegal on a board, or for that matter anywhere else, get away from it. If you want to inform someone, I submit the hoster of the site would be the one to contact, and immediately. If it's child abuse, you may be required to report it to someone who can handle the matter. If it's an emergency and obviously so, you should call the cops, but only then. Why? You're their first lead, and they're going to look at you and check you out to some degree... esp if it involves S&M and underage or other such illicit activity. They're going to want to know what you were doing there in the first place, and that's going to lead to questioning for which you'll want a lawyer present.
If you really feel like being the Samaritan and calling the law on a pic or vid that appears to be illegal, you have to make the decision of the risk involved, for you
are involving yourself.
Third, get a TOR browser. TOR is a very good anonymous network run by volunteers who donate computing power so your surfing activities can travel across the Web with almost total stealth. It's not an ISP, but it does mask your normal IP address, and multiple times. It's at
www.torproject.org , and runs with a pre-configured version of Firefox. Check it out, and surf here without the healthy paranoia! Be not afraid, just cautious...
Is it any different to be tied up vs being tied down? One of the great things about English, its flexibility :p