There was a time when the difference between a three-cent stamp and a one-cent stamp was a meaningful amount of money. That was when the United States followed the lead of other nations and passed laws permitting its citizenry to send postcards at a lower rate than letters.
Newspapers became carriers of newsworthy photography but family photographs were not newsworthy and, except for the society and celebrity pages, still are not newsworthy.
So, how did we tell our distant relatives about the family at home? The answer was to have those family portraits printed on postcard stock and mail them to your brother in California, your cousin in Texas, your aunt in New England, your uncle in North Dakota, etc.
Now, my wife and I don't have many of those old postcards of our relatives but we do have three. Fortunately, someone had the foresight to name the individuals shown on the postcards. Unfortunately, that same someone did not date the postcard. But, my wife and my genealogical records can supply us with approximate dates.
We can date one of our three postcards to "1913 or earlier" because we know that one of the individuals in the photograph, my wife's great-grandmother, died in that year. Great-grandmother is the woman seated. My wife's grandmother is the woman standing farthest to the right.
The image on the second postcard is poor due to the fading and the fact that the baby, my mother-in-law, is set against the white dress of an elder sister. We can date this family postcard back to 1907 because we know the under-one-year old infant in the picture, my mother -in-law, was born in January of that year.
We can date the third family postcard to 1932 because the subject person of the picture, my brother Joe, is dressed in his First Communion dress.
The tradition continues in a changed form. It thrives today in the form of Christmas Greeting mailers, often, but not exclusively, on light cardboard stock with a picture of all or some of the family. Some such cards may be dated. Some may contain names of family members.
My wife and I received a similar mailer last summer announcing the graduation from college of a niece. The recipient could easily justify labeling and saving these holiday and special occasion greeting mailers for the future genealogist who inevitably will crop up amongst the descendants in the family.