Photochrom photos were popular in the late 1800s and early 1900s. Photochrom was a process of colorizing black and white photos using lithograph printing.
In 1898, Congress passed the Private Mailing Card Act which let private publishers produce postcards. Photochrom postcards could be mailed for one cent each, (cheaper than the two cent letter rate.)
Publishers including the Detroit Photographic company created thousands of photochrom prints. After World War I, the popularity of photochrom postcards diminished.