The IMG tag points to off-site image storage, like Photobucket or Flickr. But if you go that route, please use the TIMG tag, or else the image is too large and takes too much bandwidth to read for those with limited connections.
for example [ TIMG ]http://i82.photobucket.com/albums/j251/jkernitzki/1903_Church_Ext.jpg[ /TIMG ] results in this (I added spaces in the code so you could see it):
You'll note that it is clickable to see the full sized version, like a local attachment.