I did with my first two children (not all the time, just occasionally - once to announce and maybe a 3D scan later on)
It wasn't until recently that I read about infertile women or those who have had miscarriages finding them particularly upsetting.
As somebody who has had two miscarriages myself (fortunately both first trimester) it still didn't occur to me.. I guess whenever I saw other people's scans, even immediately after my losses, I never equated it with my own. I was envious of them but figured their pregnancy did not reflect on my loss - the scan photo itself did not upset me.. the news itself was the tough part. My mistake was naively assuming everyone else felt like I did. It seems that for many, scan photos are actually more upsetting than newborn photos (which are also upsetting) for several reasons, but people don't mind older babies as much.
Now 27 weeks pregnant with my third but nobody on Facebook (aside from the family and few close friends we have told) knows, as I am high risk times about 3, so no reason to put up scan photos! They'll just get newborn photos as an announcement if all goes well when it happens.
If FB did know, I probably wouldn't post scan photos as I now know it would upset at least two friends that I know of (and goodness knows how many more I don't know about) but you have to draw the line somewhere and I will always put up photos of my newborns.