One photo showed a woman standing on a man on all fours; another showed a young man with the caption 'douche bag'.
But the one that outraged mums and dads most was a picture of a man with blood on his face, with the caption: "A real man loves his woman every day of the month."
The images were shown during a sex education class to 13 and 14-year-olds at Pine Valley Middle School in California, where pupils were being taught about 'Conception Myths'.
One parent told local news: "This is horrific. This is unacceptable material. That's something you can't unsee. This is definitely more than R-rated. This is X-rated."
The presentation was organised by Mountain Empire Family Medicine. CEO, Judi Shaplin, said: "We understand and appreciate that some members of our community have voiced concern about a sex education presentation delivered by Mountain Health to Pine Valley Middle School.
"We are reviewing the content of the presentation with a special attention to the specific images that have concerned some parents."