Real-Photo Postcards (RPPC) were first introduced in 1900. They were taken by both amateur photographers and by professional photographers in studios. The negatives were printed on postcard stock.
Kodak introduced its 3A camera in 1903. It was the first camera designed to allow amateur photographers to take pictures especially for postcards.
RPPC are real pictures printed from negatives, they are not comprised of dots like newspapers.
Before 1907 the back of the postcards had space only for the address. Federal law didn’t allow personal messages until March 1907. It was after this that postcards had a divided back for both the address and correspondence.