Both images above are magnified by 650%. The top image sample is a collotype image, hand-colored. The photograph in early postcards printed by collotype had very fine grain. However, collotype was not suitable for high-volume printing and it was soon replaced by offset printing from the 1910s.

The bottom image is from a real-photo postcard. It was an actual photograph printed on paper as a postcard. These are easy to recognize with their characteristic sheen or gloss. The grain is the finest of all.