Yeah Facebook & Twitter for sure, also Tumblr. But the people you're clicking on Path are in your group right? You can't just see anyone, or am I wrong?
I don't have any people in my group and I've been able to look at others' links.
Only the person who posted the photo can share it (and as far as I can tell, only at the time they post). As I understand it, by sharing it they are basically giving access to anyone who has the URL.