My two perspectives:
1. One of those pics are of my work. I don't mind. In fact, I think it is a compliment.
2. I joined pinterest. But, stopped using the sight within days. I was so afraid of infringing on someones rights, I hardly pinned anything.
3. I believe if you don't want to have something copied or shared you should not post it on the net. There are people who will take and use what they can, just because the can.