The article Monica posted is very important. As bloggers we use images that may be royalty free for our use, but we don't necessarily have the right to sign them away to another party like Pinterest.
If you use Pinterest it is best to use only your own images.
What I don't get, is that "Pinterest allows you to organize and share all the beautiful things you find on the web." This infers that you don't necessarily own the works you share.
Can they explain how you can share the works of others if you don't own it and how Pinterest can then claim rights?
What am I missing? As far as I can tell, this is a copyright nightmare.