This is a post-mortem daguerreotype – a photograph taken of a dead person. Many people now think of these images as morbid or gruesome, but I think they’re especially poignant.
Back in the Daguerreian era (1839 to ~1858), death was more routine than visits to the photographer. $5 for a photograph was a lot of money back then, especially considering the large family sizes. In addition, daguerreotypes required long exposure times – some children could not sit motionless for two or more minutes. Grieving parents often had no photographs of their child alive, so when Death stole a child, they called the Daguerreotypist.
I imagine these were among the most cherished of daguerreotypes. Some contemporary collectors specialize in collecting post-mortems. (This one is quite delicate and tastefully done – there are some pretty shocking post-mortems out there.)