Death portraits in the 1800s were expensive and only the more affluent could afford them. Those with the means to pay were often willing to, especially for infants. In an era of high infant death rates, the funeral portrait was perhaps the only photograph of a child who had died. Photographers even advertised "Post Mortem Photographs" as a specialty.
In these photos, there was often still the attempt to avoid the reality of death. The deceased was often propped up in a chair. Sometimes the monochrome photos were touched up with color, as if to deny the death pallor.
Death photos were usually done as daguerreotypes, photos on polished silver. By the mid-1850s death photos began to appear on glass (ambrotypes), thinner and cheaper metal (tintype), and paper (carte-de-visite). And by the 1860s, the price of memento mori photography was affordable by just about anyone.
Even so, not all funeral images were preserved in this way. In place of a photograph, sometimes a drawing of the dead sufficed. In the days before "Photoshopping" became a verb, Currier & Ives used the technique in a lithograph of President Lincoln's death. The litho of Abraham Lincoln shows him surrounded by people who were not even present at his deathbed such as his son, Tad, and Mrs. Lincoln.
By the 20th Century, funeral photos were considered proof of a death in murder cases pre-dating sophisticated criminal investigation and forensic methods. And there was the practical application of showing off the work of an undertaker.
Prior to that, most cultures attempted to put death out of mind. The trend changed, and continues today, with a desire to retain the presence of the deceased in any way possible. Since photographs are an effective way to do that, memento mori photography became a tradition in many cultures.
One of the more unique uses of memento mori photography exists in a cemetery in Yekaterinburg, Russia. Huge marble, granite, or malachite markers on the graves of slain mobsters have been engraved with life-like engraved likenesses of the deceased. In this case, the images used were of the mobsters at the height of youth and power. But, again, it is an attempt to use photography to remember the dead.
Most instances of memento mori photography are intended to be personal and confined to the family. While photographers in a war zone might photograph the dead, it is a tradition not to publish photos of the deceased even if the photo does not depict the violence of their death.
Memento mori still reminds us that we, too, will die. But we recognize that memento mori photography serves as a tool for grieving and of remembering.