A photographic process made by Louis Jacques Mande Daguerre in 1839. It was good for portraiture but not landscapes and you had to stay very still when sitting for pictures because of the long exposure.
In brief, his method consisted of treating silver-plated copper sheets with iodine to make them sensitive to light, then exposing them in a camera and "developing" the images with warm mercury vapor.
There are still some practicing daguerreotypists today but for the most part, the process is outdated and dangerous because of the hazardous mercury vapors. Some people prefer the alternative and less toxic Becquerel process.
"The reason why no one is similing in a Daguerreotype is because the exposure took a really long time."