There is a little "Pin it" icon under each of your cards in on a Card Details page as well as provided in your email notice when you sell a card. By clicking this icon the card thumbnail and a link will be posted on your Pinterest pinboard.
Pinterest is a pinboard-style social photo sharing website that allows users to create and manage theme-based image collections such as events, interests, hobbies and more. Users can browse other pinboards for inspiration, 're-pin' images to their own collections and or 'like' photos. Pinterest's mission is to “connect everyone in the world through the ‘things’ they find interesting via a global platform of inspiration and idea sharing.
Artists have found this to be a fantastic way to share images.