Where can I go to report offensive images/video online? (infant abuse)?

I play this game called cyber nations, it's simple enough. Anyway, someone attacked me and yada yada yada, basically told me to go to his forum and see what I had to do to get him stopped. Now I go to this forum, and they have the moderator whose icon is a video loop of some guy punching a toddler in the face, pushing him to the ground, and then kicking him in the stomach and his tag line reads beating up children since 2011. Where can I go to report this short of a police station? I'm not getting involved with police since I have no idea where this guy lives and it's nowhere near me. Is there like some sort of online website you can go to report this kind of stuff?