These web pages were created to showcase single images that may be of interest. They are called "picdocs" after the idea that each web page (document) shows an image (picture).
This website offers many other image showcases, but those are formatted as galleries, where many images appear on the same web page. The galleries are then grouped under a theme, such as the Union Pacific 4014 Steam Locomotive 'Big Boy'.
The 'PicDocs' listed here include images of mostly U. S. postal history items. These can include stamps, covers, and postcards.