click on the image in your post then click on the icon and paste in the URL for the item
Put the image address inside the [IMG ] tags, then either highlight the whole string of txt (including the tags) and click the button FOB points out above, or just type [URL ] and [/URL ] either side of the string of txt (without the spaces).
It should look like this: [URL ][IMG ]http-my-image-address.jpg[/IMG ][/URL ]
Cheers!