My first encounter with boudoir photos from the early 20th century was a coincidence. My purchase of a Taxiphote stereoscope included 74 glass stereoviews from Jules Richard's Atrium collection. I started reading about the history of erotic photography during La Belle Époque and discovered the photographs of Jean Agélou.
Jean Agélou was a French photographer who is known for his erotic photographs. His French Postcards were very popular in the early 20th century, but he also created stereo photos.
Erotic photography is almost as old as photography itself. Stereoscopic images of nude females were made by photographers like Auguste Belloc and Félix-Jacques Moulin in the 1850s. Erotic images became widely available in the beginning of the 20th century.