As photograph styles changed through the 1800s, you can learn to identify the different types of photos and put a rough date on them based simply on their format.
As discussed in an earlier article, one of the ways to date an old photograph is to see what kind of photo it is. In other words, examine the paper, backing and format of the photo and you will be able to get a rough idea of when the photograph was produced.
During the early years of photography, there have been basically 3 overall types of photographs (in terms of materials they were printed on): paper and cardboard, metal or glass. The most common are photos on paper, and their main types are the Carte-de-visite, the cabinet card and the photo postcard. Metal photos were either tin-type or daguerreotype, and photos on glass were likely ambrotypes. Each type of photo has a time-frame and use associated with it. Since the metal/glass photos are relatively rare, this article will focus on the more common paper/cardboard varieties.
These are specifically photos that would have been taken by a professional photographer, since home photography equipment wasn't readily available. Once people started taking their own photos, many of these distinguishing features vanished, and you will have to date photos by the image itself.
Also referred to simply as cartes. These small photos were glued to a cardboard backing that was about 10cm by 6cm in size. The size was constant because photo albums of the day were made with holes cut in the stiff pages to hold these carte photos. The backing card was usually decorated with the name of the photographer, along with some decorative flourishes. The earliest cartes are from 1859, and had square corners. In order for the photos to slide smoothly into the albums, they started being made with rounded corners around 1872. But the square corners did come back again later in 1900, possibly as the use of albums became less popular. The card backing was quite thin with the earlier photos, and got heavier as the years progressed. Those made after 1880 were very thick and sturdy. Carte-de-visite stopped being produced in the early 1900s.
A similar style and design of photo as the above described cartes, but larger. Also mounted on cardboard backing, these photos also showed the name of the photographer on the back, or under the photo on the front. Cabinet cards were about 16 ½ cm x 10 ½ cm in size. Cabinet cards date a little later than the Carte-de-visite, being first introduced around the late 1860s. Most of them are dated from the 1870s though. These photos always had rounded corners until 1900, when both rounded or square cards were produced.
I'm sure the name explains this one. It became popular to have photos printed directly on cards that could be sent through the mail, as a convenient way to share photos with friends and family. These cards are around 14cm x 9 cm, and have obvious postcard markings on the back. If you're lucky, a used card will have a dated postmark. Photo postcards were being made in the very early 1900s, just as the other styles of photos were losing popularity. They continued in production as late as the 1940s and 1950s.