Facebook loves to test experimental new features with small groups of its users, and today brings another one: snail mail postcards made out of your Facebook photos. The social network is teaming up with Sincerely, the guys behind Postagram, to process and deliver the postcards. In order to place an order, you click the "Mail Postcard" button next to the "Tag Photo" button inside the Facebook photo viewer. You can write a message, attach an address, or ask a friend for their address if you don't have it. One thing you can't do is send public photos or photos from Facebook Pages.