The collecting of picture postcards called deltiology has been a popular activity for more than a century. Because of the vast volume of postcards, individuals who collect them usually confine their collection to postcards depicting a few specific subjects. The extensive construction of new library buildings in communities across the United States in the first two decades of the 19th century coincided with the heyday of picture postcards and libraries were a frequent subject of these postcards. So it is not surprising that some individuals collected postcards with libraries as their subject. I've been collecting library postcards for more than 25 years and I have amassed a collection of several thousand of these cards. That is not a particularly large collection in the history of library postcard collecting. I am aware of two library postcard collections that exceed 25,000 cards and several more that exceed 10,000 cards. At any one time there are almost 40,000 library postcards listed on eBay. Because of the large number of library postcards it is prudent to specialize if you are interested in this collecting area. There are many possible approaches to collecting library postcards and it is entirely up to each individual to determine the approach they will take.
I collect primarily (but not entirely) postcards related to United States libraries. A collector can choose to collect worldwide libraries or the libraries of other selected countries. It is also possible to narrow the focus of a collection to the libraries of a particular state or city in a country. I have a comprehensive collection of Wisconsin library postcards. There can be multiple different postcards of a particular library and a collector can focus on a single library or group of libraries. The Library of Congress, the New York Public Library, and the Boston Public Library are all depicted on many different postcards. I have a good collection of Library of Congress postcards. There are other broad categories of libraries that can be the focus of a library postcard collection. These include among others - public libraries, academic libraries, special libraries (law, medical, historical, government), and Carnegie libraries. My collection includes all of these but has many more public libraries than any other category.
There are several other ways a collection can be narrowed or focused. These often determine the cost of the postcard. A collector will need to decide if they will only collect unposted postcards or will include those that have been sent through the mail. I collect both but prefer those that have actually been sent through the mail. I particularly value cards that have a message from the sender related to the library depicted on the postcard. The image depicted on the postcard is important in determining value. Images on the exterior of a library building with few additional features are most common and least expensive. Interior views of a library are far less common. Additional image features including people and vehicles add cost and value. Library postcards which show people inside of a library are particularly hard to find, and are among those that I personally value the most. Some other categories of library postcards that I collect include: postcards of the American Library Association Library War Service in World War I (and other military libraries); postcards depicting bookmobiles, postcards depicting state libraries, leather library postcards, and a variety of other unusual library postcards.
Library postcards are valuable in researching library and architectural history. Bernadette A. Lear has an excellent article on this topic. “Wishing They Were There: Old Postcards and Library History.” Libraries & the Cultural Record, vol. 43, no. 1, University of Texas Press, 2008, pp. 77–101,
Hans Krol a retired librarian living in Heemstede, Netherlands has the largest library postcard collection in the world and continues to add to his collection. It exceeds over 25,000 postcards. Krol has an amazing blog which includes images of some of his postcards. Krol is a collector of a broad range of librariana (library collectibles), and is a founder of the Bibliotheekmuseum (Library Museum) that is located in the Bibliotheek Amsterdam (Amsterdam Library).
Norman D. Stevens also assembled a collection exceeding 25,000 library postcards. His collection includes a number of smaller collections that were previously assembled by several other individuals. Stevens donated his collection to the Canadian Centre for Architecture (CCA) in Montreal, Quebec, Canada where it is now located and is part of the Norman D. Stevens Collection of Library Architecture.
Judy Aulik's "Civic Pride in a Lost America: Library Postcards" website has one of the most extensive and informative depiction of U.S. library postcards on the web. She has a collection of close to 8,000 library postcards with a heavy emphasis on public libraries and Carnegie libraries. Many are displayed on her website.
Dan Lester accumulated a collection in excess of 10,000 library postcards before he stopped collecting. He donated the largest portion of his collection to the American Library Association Archives. The story of how his collection got to the ALA Archives is told HERE. A description of the Lester collection and other postcard collections at the ALA Archives is located HERE.