Mourning is a strange thing, and different cultures deal with it in vastly different ways. But there are reasons people associate the Victorians with morbidity and death, and one of them is memento mori.
The fact is, postmortem photographs like this were taken more than any other kind of photograph in the Victorian era -- especially in the U.S. -- and in many cases these carefully arranged, meticulously staged pictures were the only ones ever taken of their subjects. From Stanley Burns' book Sleeping Beauty: Memorial Photography in America:
These photographs were a common aspect of American culture, a part of the mourning and memorialization process. Surviving families were proud of these images and hung them in their homes, sent copies to friends and relatives, wore them as lockets or carried them as pocket mirrors. Nineteenth-century Americans knew how to respond to these images. Today there is no culturally normative response to postmortem photographs.
So, given your lack of a "culturally normative response" to these pictures, dear reader, we advise the faint of heart among you to click elsewhere.
From PBS.com: "This portrait appears to have been taken in the formal parlor of a family home. The parlor, or "death room," was an important part of funerary rituals for most of the 19th century, the place where deceased family members were laid out for final respects. This image dates to c. 1890-1905, a time when many funerals were still taking place at home. Soon, however, death would begin to leave the home and by end of World War I most Americans will receive their health care in doctor's offices and hospitals and most funerals will take place in funeral homes. As the funeral "parlor" came into vogue, the home parlor was rechristened a "living room." A 1910 issue of Ladies Home Journal declared the "death room" to be a term of the past."
Also, did you notice the strange silhouette on the right side of the picture? That's the photographer's assistant, holding the casket lid open for the shot.