I like to camouflage my links on social site at about 20 percent mine and the other 80 percent is relevant but someone elses. Frequently I will find a good article and share it to all the sites. My sites are linked. Will Google see this as duplicate content or will it see me as sharing my finds with a different group of people. For example, you may tell the same fishing story to your buddies at work, and then to your friends at church, and then to the guys in the bar, and on and on. All using the same story. Would Google see this as duplicate content.
We did not sign a "Terms of Use" policy that would prohibit these pictures from being posted or that would have given this 'gentleman' the authority to do so.
I know, I've shared the same links throughout various groups and pages on Facebook. With the same titles and all. It's all good, if I'm getting this right. If you have a link - sharing it with a relevant community shouldn't be considered spam. That's why use the Facebook function (Share button) to spread the word. Don't just spam random places with random links. As for the aspect of sharing the same story through multiple sites. You have to be careful. Research cannonical links and how they can help you out with this. Simply copy-pasting content is really bad.
This is a really interesting question. @alex is explained perfectly but I can't say anything without seeing your site because I don't know, is that social site like Facebook, google+ or money making social sites, full of contents and entertaining images.