- Copy the address (URL) of the Image file (highlight & CRTL+C in your web browser's address bar)
- Click the 'Img' button in the forum post-editor window
- Paste the copied URL between the img 'tags' in your post
Then submit your post.
Your image will be placed directly into your post, like this:
![Image](http://upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Matt_Green_1.jpg/200px-Matt_Green_1.jpg)