Undivided Back - Publishers were allowed to use the word POSTCARD on the back, but no
writing was allowed on the non-picture side, except for the address; space was left around the image on the front side for a message from the sender. Postcards from this era are still readily found with dealers at postcard shows, in antique stores, in your grandmother's attic, and can be obtained at a reasonably modest cost.
Divided Back - Postcards could be printed with a vertical line on the back, with the area
to the right of the line for the address, and the area to the left for a
message. Most cards were printed in Germany, and
the lithography processes were so advanced that most cards from this period are
spectacular. Postcard sending and
collecting became a mania, and this collecting frenzy was only slowed by World War I which cut off the supply of the quality cards from Germany. This printing style still exists at present.