Posted By:
Hankron
For example, on this typically-styled cabinet card you can see how the rectangular photographic print is pasted to the larger carboard mount. And, as is common, the photographers found the extra space at the bottom suitable to put a little advertisment/credit for the studio. The mount and photographic print will come in wide variety of shapes and styles, but the mount will usually be larger.
In the 20th century, the photographic paper slowly became thicker and sturdier, so mounting wasn't neccesary. The cabinet card and simularly mounted photographs were continued in the early 20th century (ala 191? T5 Pinkerton Cabinets), mostly for style reasons ('mounted photos are fancy'). So, by the 1910s you will find both mounted and unmounted photographs.
Early 1900s: An unmounted (no cardboard backing) Ty Cobb photo and a mounted (cardboard backing) Joe McGinnity