Charles Armstrong's postcard to his father (December, 1906)
is an example of an early real photo card. While the law
prevented the sender from writing on the back of the card,
nothing prevented him from writing a message on the front.
This unmailed card of Vivian Miller (rt.)
and a friend can be dated by the AZO
stamp box: 4 triangles pointing up tell us
the card was printed between 1904-1918.
Vivian was born in 1902, so this photo
was probably taken in 1917 or 1918.
There a number of other clues on postcards, RPPC or other, which can help you date the card. For example, if you knew someone in the family was born in 1905, but didn't know when she died, finding a linen postcard written by her or to her helps you narrow her death to between 1930-1945, when linen postcards were issued.
You can learn about other clues to be found on postcards, as well as the history of postcards on a number of websites, but here are some recommendations:
- The Postcard Shoppe Postcard Identification
- The Smithsonian Institution's Chronology of the Picture Postcard
- Webfooters Post Card Club