Mirror, Mirror, On The Wall...
These constitute some of the earliest erotic photographs and were produced by the time-consuming process of daguerreotyping, in which images were printed onto the mirrorlike surface of silver-plated copper. As you might expect, most of them were of French origin (like the majority of early erotic photos) and date from the 1850s-1880s.
Daguerreotypes have a very unique look that's frankly got to be seen in person for the full effect - surprisingly sharp images on a reflective surface, with nuances of light & shade that give them a depth lacking in simple print photography, and colors were hand-tinted by artists themselves. "Atmospheric" or "moody" is often an apt adjective. These digital copies don't really have the visual impact of a well-preserved daguerreotype seen in-the-flesh, but we've tried to preserve the same color range that gives them some of their ambience.
The damoiselles herein were primarily artists' models, as you can somewhat glean from the poses, and it's true that many of these images were marketed as "artistic references" for drawing or painting from. That they were also beautiful naked women to ogle was an unspoken (though usually primary) benefit.
The girl depicted in the first of these daguerreotypes is rumored to be French writer Emile Zola's mistress, and perhaps one of the inspirations for the character Nana in his eponymous novel. That's the story anyhow.