Lets say that as a user you post a number of copyrighted photos on your Pinterest page and at the same time it is easy (link to your own site, Facebook page, ...) to track your idendity.
Could the copyright owner sue you, file for damage claims and possibly win?
The content is not on your server but you, as the user, made the infringement possible. What is the (legal) difference between this and illegal music downloads and distribution?