"After the invention of daguerrotype, the memorializing habits of people have changed: theyve chosen the cheap, higher quality photographs instead of expensive and not so lifelike paintings. Painting dead people was common for centuries, so its no surprise that, in the Victorian Era, post-mortem photos also came into fashion. Here are some of the strangest ones."
From the time daguerreotypes became available c.1839, Memento Mori photos were a way of honoring & remembering the dead. The practice faded after about 1900 as cameras became common & people were likely to have other photos taken during life.