You can use the attach tag:
[ATTACH=full]ID#[/ATTACH]
But it won't show inline outside of the original post. Rather it will show a hyperlink to the image.
Or you can use the URL of the attached image with an IMG tag. For example:
[IMG]http://www.yoursite.com/forum/index.php?attachments/filename-gif.ID#/&embedded=1[/IMG]