Say if I own a blog site for multiple users like wordpress, say blogsss.com, and every user hosts their blog under a subdomain *.blogsss.com.
UserA post a JPEG that UserA claims it is under Creative Commons, but actually it isn't.
Then UserB, C, and D use that JPEG, without knowing it is actually not under Creative Commons.
A few months later, the rightful owner sues my site for copyright infringement, and asks me to remove the image and pays a hefty penalty fee!
What should I do to ensure that my site and I won't get sued?