You and me both. My wife (!) showed me 3 times how to do it and I still fail, and now she's away for a time.
So I'm going to try it now:
- First, I right click on an image. I'm using Underseer's avatar, because it's handy.
- Then click on COPY IMAGE LOCATION. Now my clipboard knows where Underseer's avatar is.
- Now I'm gonna click on the icon that looks like a picture. It's just above this composition window, between the little film strip and the red X. If I hover over it first, it says INSERT IMAGE.
- Next I have to choose between two tabs. Since I'm ready with a URL, I click on the one that says, FROM URL. Then I paste (control-V) the image's URL into the obvious place.
- Then, because I'm using oversize text, I have to grab the top of that popup window, and drag the window high enough that I can see the button that says OK. I click OK, and, sure enough, here's Underseer's avatar: