Both sites accept "BBcode" which will allow you to link to an image somewhere else on the net. To add an image you'd enter:
[ img ] http:// your.imageURL.here.jpg [ /img ]
without the spaces.
This also goes for [ i ]
italics [ /i ], [ b ]
bolded[ /b ], etc. (again, no spaces).
However it looks like if you want to have us host the image, it'll have to be as an attachment. Good for people with dial up (they don't have to download the image unless they want to), but otherwise a little clunky.
Don