As you apparently are aware, the images at the bottom of the message body are done as attachments as you submit your message.

The images that are spread throughout the text are "linked" images, the image is hosted at a different location.  If you have images hosted somewhere that you would like to link, when preparing to post, use the "insert/edit image" icon.  The icon appears as a small green tree on the WYSIWYG editor bar.  Clicking that "tree" will take you to a window that allows you to paste the link to your hosted image and INSERT it into your message.

I just remembered - there is a tutorial on the subject here:

http://www.newagtalk.com/faq/image-tutorial.htm