After reading your problem, the $home variable really
serves to save you from giving yourself carpal tunnel syndrome
from typing out the full path.
For a moment, let's say you keep all your images to your
site in the filesystem path /home/username/www/images/.
Your web-based path to the script might be /cgi-bin/showpic.
Now you want to log who is visiting each of your pages using
this script without putting the same image on every page.
You could then set $home equal to
'/home/username/www/images'. Then for each image that you
want to have generate an entry in the log, you would set
the src to '/cgi-bin/showpic/myHead.jpg' or
'/cgi-bin/showpic/myHouse.jpg' or whatever.
However, if you have images all over your filesystem,
you might set $home to '/home/username/www'. Then you
image src could be '/cgi-bin/showpic/images/myHead.jpg' or
'/cgi-bin/showpic/britain/bigben.jpg' or any other image
you have on a page you want to log.