Are you trying to add the pic through the common method - click the Insert Image icon, choose Browse, find your image, click open, choose size, click Insert Image? I believe if you are using the app, you do not see the icon bar, so it might be worthwhile trying through the Classic Site.

Apparently this is a common problem, though I have never had it happen to me. Sometimes it seems to be a browser problem - are you using Firefox?(which apparently can again sometimes be a problem though I just did one OK using Firefox)