Image attribution has been something of a sticky subject for Pinterest and by their own admission, it's something that they're still working on to get right. While earlier in the year they launched a 'do not pin' option with Flickr, they've now taken this the other way with an embedded pin it button within Flickr. The option is available within the share menu on Flickr:
Now when you pin an image on Flickr, it will automatically be populated with the name of the photographer, their title for the photo and a link to the photo page. Users won't be able to edit this section so photographers can be sure their images will always be correctly attributed, no matter where they're being repinned on the site.
Importantly, this also applies if a Flickr image is repinned from a third party site, provided it has been correctly embedded.