I frequently paste in screenshots from Windows snipping tool: "Snip & Sketch". Usually they are just a portion of a screen and to make it clear that it is an image I always use the Thunderbird Image Properties dialog to change the "Appearance" by specifying a 1 px border line around the image. But I have to do that every time. It would be great if it remembered my settings and always put a line around images when I paste them in.