The only way to do that (since you want to avoid attaching/upload), is with the [img][/img] tags. The pics you want to do this with have to be on the internet somewhere already. Find out the URL (http address) of the file and insert it like so --> "[img] http: // filelocation[/img]" (remove the spaces) anywhere in your message and that's where it'll show up.
If you can't remember the "[img]" tag, then in the editor, click on the little mountain icon and it'll prompt you for the location of the image file. Then just insert the URL.
Hope that's clear.