I have a very successful website which is an authority in its niche. I am considering adding forums and image galleries to this website under a separate sub-domain.

I expect lots of public participation in the forums where they can discuss anything under the sun, except porn and sex. The image gallery would be where users post their photos.

Would it be advisable to start these sections within the sub domain of the same successful website or get a completely new domain for them.

My concerns are: what if someone posts copyrighted images and it might cause a problem for my website. What are the rules regarding this? If someone posts a copyrighted image and if the copyright owner comes to know about it, what are my liabilities?

Would he first request to get the image off my website or sue me without any such request? Can he get my entire website down or only the sub-domain?

Since the website would also have forums, would discussions on controversial topics or otherwise be problematic?

I need as much clear information on these as possible, so I can take decision on whether to start these sections on the same website or a totally new website. I do not want my successful website to be affected because of these new sections.