Sources Facebook store photos for there User reshared by Pinterest User
#Facebook Image Server
https://pinterest.com/source/a1.sphotos.ak.fbcdn.net/
https://pinterest.com/source/a2.sphotos.ak.fbcdn.net/
https://pinterest.com/source/a3.sphotos.ak.fbcdn.net/
up to
https://pinterest.com/source/a9.sphotos.ak.fbcdn.net/
You get a good impression what photo style and content is posted and liked on Facebook and vice versa.