Thus by promoting and participating in copyright infringement, Pinterest lays claim to the intellectual property of others such that they can make money with it if they so choose, all of which is based on assuming its users have the rights they are transferring to Pinterest when they post content. That is, when they post someone else’s content, which represents the vast majority of the images shown on the site.READ the whole article
From AMD Law Group:
Although many Pinterest users do not claim to own any of the images that they publish, it is still copyright infringement to not seek permission from the content’s creators. It’s copyright infringement even if you do link back to the original creator’s site or credit them. Unless you seek permission before you share someone else’s image, you violate the right of content holders to exclusively redistribute their material.