Daguerreotype photographs were popular from the early 1840s until about 1860. Daguerreotypes therefore pre-date the Civil War.
Daguerreotypes are named after a Frenchman Louis-Jacques-Mande Daguerre, who perfected the process that led to the first permanent photographic image that bears his name. Daguerre published a manual in 1839 that detailed the process.

Daguerreotypes involve a positive photographic image on a thin copper plate that is coated with highly polished silver. You cannot see the copper plate due to the silver coating. They are most often found in hinged wooden cases covered with ornate leather or paper. The case is designed to protect the delicate image. The image itself is usually sealed into the package and covered with glass to protect it.

A daguerreotype can look like either a positive or negative image, depending upon the angle at which you view it. The best angle for viewing the image is straight on. View the image from any angle tends to make the image turn negative or will cause it to disappear entirely. A daguerreotype image almost looks like an etched mirror. An image in good condition is amazing detailed for the first permanent photographic process.

The Daguerreotype process involves taking the silver coated copper plate and placing it in a box where it is exposed to iodine vapors. The plate was then exposed in a special camera. Exposure times could last 5 to 30 minutes, which explains the deadpan expressions on the faces of many subjects.

Something that added to the discomfort of sitting absolutely still for lengths of time was a device called a headrest, which was a U-shaped support mounted on a metal stand or the back of the sitting chair. You cannot see the device in daguerreotype photographs, but the heads of the subjects were resting against the metal headrest, which kept them from swaying or moving while the daguerreotype plate was being exposed. One thing that is noticeable in daguerreotypes taken of children is that they are almost always blurry due to the difficulty with getting children to sit still.

After exposing the plate, it was placed in another box where is was exposed to heated mercury vapors. This developed the image, which was then made permanent with a bath of hyposulfate of soda. By the end of the 1840s, the components in the process were mass produced and improvements were made that reduced the exposure time and improved the image quality.

By the mid 1840s there were thousands of artists working with the daguerreotype process and by 1850 there were daguerreotype studios in all of the major cities throughout Europe and the USA.

The most important issue if you have a daguerreotype images in your family history collection is the narrow date range in which they were produced. Daguerreotypes were produced in the 1840s and 1850s. By the 1860s, other processes emerged that were easier to work with, and daguerreotypes fell into obscurity.