Image problems.

I added Your Guestbook software to my site, and over all, it's great, how ever, when I got it, it didn't show any images. I had to check and see the problem, and couldn't find it, so to fix it I had to remove portions of the script. I removed the varibel "$GB_PG[base_url]" from every link in the script, because it seemed to be the problem. Before I did this, the image's properties showed that the URL was like HttP://picture/image.jpeg, and didn't show the domain. After I removed that varible, the image appeared correctly.
However, now user images don't seem to appear any more. I think that in order to overal fix this, is to fix the source. But I don't know where the source is. I am guessing that where ever the $GB_PG[base_url] varible is, is the source. how ever, there are alot of files, and text to read trough. I'd like to know where is the $GB_PG[base_url] started?

Base Url is set in the config.inc.php file.