I have a photo website. 15% of the photos belong to approved registered users. They agree my terms about uploading their images in my web pages. I include a photographer credit on right bottom corner.
About identifying the site with google, every page contains a google+ button to MY google+ page it also contains
<link href="https://plus.google.com/nnnnnnnnnn/" rel="publisher" />
I need some advice in order to respect google rules about my pages containing other photographers images not to be penalized because of possible duplicated or interpreted as stolen content. My concern is also about adding G+ links (to MY photo page) and Google publisher id would harm my site rank because of pages containing third-party photos.