Some useful API endpoints you can use to retrieve pins from an user’s profile or specific board :
https://api.pinterest.com/v3/pidgets/boards/[username]/[board_name]/pins/retrieves last 50 pins for a specific user’s board
https://api.pinterest.com/v3/pidgets/users/[username]/pins/retrieves last 50 pins (globally)
http://i.pinimg.com/originals/[xx]/[yy]/[zz]/[xxyyzz...].jpgretrieves the pin in its original size (this URL format is returned by the previous methods)
Pinterest hasn’t released a public API yet, and the API key seems to be hard to get.
Edit: I used these endpoints in my Pinwatcher script that allows you to backup & save your or someone’s pins to your hard drive.