The forum software behaves in a slightly different way to vBulletin (as found on several other forums).
Inserting an inline image from a linkAssuming you have the link to an image on your clipboard, click the Insert Image button
and paste the image link where the cursor is positioned, between the tags ...] and [... Please keep try to keep in-line images at 640 pixels wide or less.
Adding an image (or other file) as an Attachment To add an attachment (note you you can't use the Quick Reply box). Under the text entry box there's a link
+Additional Options... Click on it, then use the control in the
Attach: section to locate the file in your computer.