With the 1908 volume of his treatise Le Corset, Dr. Ludovic O’Followell hoped to make clear the detrimental effects the then-current corset designs had on women's health. To that end, he took X-ray images of women in their binding underthings.
According to the Public Domain Review, O'Followell wasn't looking to ban corsets entirely, but was hoping to promote a less extreme design. (In fact, O'Followell wrote a column for a high-end corsetier magazine.) Le Corset offered X-rays and illustrated diagrams of the ribcage and organ displacement these corsets created, and pointed to problems in the respiratory, circulatory, and digestive systems that could be caused by daily use of severely cinching corsets. Images from Le Corset, including medical illustrations of the impact of corsets on rib bones and internal organs as well as X-ray images of women's torsos sans corset, are on display at Wikimedia Commons, and the text is available en français at Wikisource.
Edit: I'd just like to point out there are some great discussions in the comments from modern corset makers talking about the differences between early 20th century corsets and modern ones, the advantages of certain types of corsets, and how fashionable posture, aided but not caused by corsets, impacted women's health.