The pin-up images could be cut out of magazines or newspapers, or be from postcards and so on. Such photos often appear on calendars, which are meant to be pinned up anyway. Becoming later an instant hit being mass-produced.
An early example of the latter type was the Gibson girl, drawn by Charles Dana Gibson. The genre also gave rise to several well-known artists, including Alberto Vargas, Gil Elvgren, and George Petty.