Collecting postcards was a natural extension of the Picture 
Collection's mission to provide its users with visual material in a variety of formats. Postcards were circulated from at least the early 1920's and were likely housed with subject clippings files until later segregated into a separate collection. Acquisition has been mainly through donations from hobbyists and travelers, but the department has historically sought ways to harvest ephemeral material of this kind; librarians on foreign or domestic travels, for instance, are encouraged to buy and add postcards to the collection.
In addition to the digitized domestic holiday postcards, the Picture Collection also digitized foreign postcards for Easter, Christmas, and New Year, among which one can find Bulgarian, Czech, Polish, and Russian holiday postcards.
See also a blog "Christmas Postcards from Central Europe."
