Mr_Grubby/Sabredog,
Let us assume that your "picture" has an exclusive URL reference, that is, it is not buried in a page of text. It may have the three letter suffix ".jpg" or "gif". If you haven't sussed it yet, if you "right-click" your mouse, with it positioned over the picture, then select properties, this will give you the "exclusive" URL reference for the picture.
Cut and paste this URL reference into your message. At the beginning of the URL reference put "[img]" and at the end put "[/img]", without the quotes! This should do the biz.