nas,
The image has to be either already on the web somewhere, or you need to upload the image to your website.
Geocities gives away free webspace --not all free webhosting services allow UBB to 'refer' to images they host, but Geocities is one.
Anyway, let's say your website has the image in place, you just need to use the image's exact address. Take Spot the Eel, our logo at top left of this page. If you right-click on it and select properties, you'll obtain its address:
http://www.thereeftank.com/ubb/eel.jpg
I just bracket that address with the IMG command, like so:
{IMG}http://www.thereeftank.com/ubb/eel.jpg{/img}
except I use [] instead of {}brackets. Leave no spaces between the commands and the address at either end! Here's the result.
To see exactly what I did, you can click on the edit message button of this very post of mine. You won't be able to edit anything, but you'll see exactly what I typed out to get the final result.
Beware the Dark Side,
dark horge