Zapped (1982)
https://www.imdb.com/title/tt0084945
Actress Heather Thomas (Jane) refused to shoot her nude scenes for what was going to be her motion picture debut. In post-production, the producers inserted close-ups of a topless body double without Thomas' knowledge for Thomas' topless scene at the prom, and pasted her head onto a topless body double in a photograph shown in the movie.
These changes led Thomas to file a complaint with the Screen Actors Guild. These changes violated SAG rules giving an actor or actress the right of approval over any body double that may represent them. As such, a disclaimer at the end of the film was added which read: "A double was used for Miss Thomas in her nude scene and in the photograph."
For the prom scene, you can easily tell a body double is used.
... The topless actress does not show her face.
... She is not wearing a white pearl necklace.
... She has much darker hair than the blonde Thomas.
... Her breasts are quite smaller than what Thomas appears to have under her prom gown.
Here is the scene and my comparison of Miss Thomas to the body double.