It's called postcrossing, and you can learn how to do it by Clicking Here.  Seems like it should be called postcarding, but that's just a trivial one of the many things I don't understand about human behavior.   As you may know, I also do geocaching, benchmarking & letterboxing.  PostCrossing is an activity where you send postcards to people chosen at random all across the globe  and, in return, different randomly chosen people send you cards. 

These are cards I have received.  You can display cards you receive on the postcrossing website (which I do) but you are restricted to images too small to see clearly.  Also, you can only show the card face itself and I find the postmarks as interesting as the cards, so I'm doing this page to display the cards I receive.  I just started this recently and don't have many cards.  Serious carders have thousands.

When you click on one of the thumbnails below you'll be taken to a larger picture of the card.  Once there, you can use the navigation bar at the top of the screen to move through these larger images. 

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