I have worked with this wonderful plugin when it first came out. Yes you can display images too, however I didn't wanted to use GD and put any extra unnecessary load on the server. One other option you can use is, create images for 0, .25, .5, .75, 1.00..... to 5.00 or in many way you like it and set up the code to display image using the plugin. In this way, you will be able to display logo+image rating on an image with pretty good accuracy.
You might also want to look into other plugins Andy have developed. A good combination of them, can literally turn GLinks in a feature rich mega portal.
Hope this helps.
Vishal
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