For you the important part is informing us what happens to the data with a Privacy Policy, and I would also have a Terms of Service requiring uploaders to acknowledge the rights of others, including privacy and intellectual rights.
You can put a "By uploading an image you agree to our Terms of Service and Privacy Policy" text on the website with the links. This is not a legal advice of course, I cannot be sure that this makes your Terms of Service enforceable, but this is how others like Imgur do it.