Andy,
Geocities will not let you link directly to a .jpg from outside of geocities. Try putting the pic on a html page then reference the .htm from The Guage. That will then allow the pic to be viewed. This implies you cannot have any pics from geocities displayed/included in your posts of The Guage. It may work for you if you have referenced the pic from a geocities site, and the pics still resides in your browser cache.
TOOT!