Forum Moderators: not2easy
Like piatkow said your local laws are what you need to look at. Advice given here is general information, talk to a lawyer if necessary.
What do your sites terms and conditions state? This will help you in a dispute. Make members aware that anything they upload may be scrapped and used in other places. State that you are not liable if that happens. Also state that the pictures are the property of the uploader and using them without permission is not permitted.
Develop a Terms of Service (TOS) which STATES UNEQUIVACABLY the uploaders are responsible for their copyright/trademark (different thing) protection.
There's legal weasle words (meant in a GOOD WAY!) that make this all work and it will take an attorney to get that right. And even then you will have to sit down with that attorney to make it PLAIN SPEAK.