|An old fashioned pin board|
Pinterest claims that once a person posts (or pins to a Pinterest bulletin board) it becomes their property.
Legally all images created by you are your intellectual property. No one can take that away from you. But now it seems that Pinterest, using a third party (the pinners of sites with Pinterest), believe they can take it from you with no impunity.
Anyway if my words above seem a bit confusing I have found an excellent article on this very subject. It is well worth your time to read if you are either a Pinterest member or anyone that puts images on the web such as G+, Facebook, Blogspot, or like media.
Here is the link that explains this mess in human terms.
Pinterest -- Copyright Infringement Made Cool, by Bob Vishneski