Recently I've been looking at postcards from a postal history point of view as my knowledge increases - its a never ending field! I found this card recently and consider it a quadfecta - a lot of fun for less than 50 cents
I don't generally collect post cards, though a number of them have found their way in. But when I see post card dealers at stamp or old paper shows, I always turn the box of cards around and search via the back. I do get a few looks.
The "front" of an envelope typically contains the address and postage; the back side has the sealing flaps Thus logically, the "front" of the postcard contains the address, postage and often a message with the picture on the back side. BUT try to tell that to a postcard dealer!