Several years ago a friend was trying out my camera and took a couple pictures of me that I liked. I looked at one on a contact sheet and decided to use it as a profile picture on a site. Luckily the software reduced the number of pixels in the photo.
A couple of years later the company contacted me and asked me to provide the picture again in a higher resolution. I started to send it over again, but decided to crop it for the correct size. When I opened it there I sat wearing a women's white shirt with a pretty white lace bra. The shirt wasn't that obvious, but the bra strap and lace cup was.
I went out and looked at the one on their site and realized that you could see my bra if you knew what you were looking for. I cloned out the bra, reversed the image so the shirt opened to the right and happily sent them a new picture.
The incident came back to me because I was at a neighbors party and pictures were taken. I had on a black sweater and light nude bra which didn't show while looking in the mirror. While compressed nothing showed but looking at the image zoomed in I could easily see the bra. Experimenting a little I looked at some of the women there. In several of the pictures I could see their bras. I then called up a high resolution scan of a group of women taken in the 50s and could see some of theirs.
So be careful of what you post.