Well...I was about to link you to a tutorial to do just what you're asking, but I'm darned if I can find it.
Anyway...here's how I do it.
firstly, upload the image to a web image hoster....I use Photo-bucket, then, when the image is uploaded, open it and click on the 'IMG' entry in the box-menu of links (usually just to the right of the image). Clicking on it, automatically copies it....then all you do is copy and paste it into your message.
Sounds complex, but it's quite easy once you've done it a few times.
Les