Michael Koch, 26, posted the photos, taken between May 2016 and November 2017, to a Russian photo-sharing website, according to the St. Charles County Prosecuting Attorney's Office.
Koch posted 175 photos of women in various stages of undress on the site, Fox 2 St. Louis reported, citing court records. Investigators said 41 photos of unidentified women are believed to have been taken inside private tanning booths at Club Fitness in St. Peters, a St. Louis suburb, the station reported.
In one instance, Koch was seen holding his cellphone over a partition separating his tanning booth from that of a female customer, the St. Louis Post-Dispatch reported.
The suspect worked at the fitness club from 2010 to 2017, according to Tribune Media Wire.
The photos included six images of his girlfriend nude and engaging in sexual acts with Koch, the St. Peters police detective told the Post-Dispatch. The girlfriend told police she was unaware the photos were taken and posted online, the report said.
Koch also photographed his sister with a hidden camera when she was fully nude, the paper reported, citing court records. The photos appeared to be taken in the bathroom of their home in O'Fallon, police told the paper. The sister told police she did not know she had been photographed and had not given permission, according to the Post-Dispatch.
Koch was charged with two counts of invasion of privacy and one count of attempted invasion of privacy, Tribune Media Wire reported.
He posted $15,000 bond and was released the same day, Fox 2 reported.
Michelle Micheletti, director of marketing for Club Fitness, issued a statement to the station.
"Club Fitness takes every measure to ensure the personal privacy and security of our employees and members. Should there be any suspicions or reports about inappropriate actions or privacy abuse, we will contact the authorities immediately," she said.