I have added a Pinterest blocker on this blog and here is why: Any images that are scraped from your site and put onto Pinterest become the property of Pinterest. While Pinterest asks people to ensure that they own the copyright or that the images are free of copyright, the site’s software removes all metadata from the image thus potentially absolving Pinterest on the basis that they had no way of knowing that the image was copyrighted by someone other than the poster.
Anyone who derives income from the internet – especially from the images they produce would and should be upset if their images being sold in one domain turn up being given away by another site entirely. While Pinterest has (yesterday) changed its terms of service to indicate that they no longer reserve the right to sell your images it is disturbing to say the least that it was in there in the first place.
I use a WordPress plug-in to achieve this end. Flickr has settings in the privacy component of your profile to block other sites from sharing without your permission – at least Flickr ‘gets it’ and allows users to set the copyright and share settings as befits the user’s wishes.