What is the primary characteristic of daguerreotypes?

The primary characteristic of daguerreotypes is that they require the subject to remain still for an extended period. This is due to the exposure time needed for the image to be captured on a light-sensitive surface. Daguerreotypes were among the first forms of photography, introduced in the early 19th century, and the process often necessitated exposure times that could last from several seconds to several minutes, requiring subjects to be motionless in order to avoid blurriness.

The other options do not accurately represent daguerreotypes. For instance, they are not created on a tin plate, as daguerreotypes are made on a polished silver-plated copper sheet. Additionally, daguerreotypes do not use emulsion plates for development—this technique pertains to later photographic processes. Lastly, daguerreotypes are not a digital photography format; they are an analog photographic method that captures images through chemical reactions to light on a physical medium.