Ico
From Hackepedia
To create a Windows icon .ico file, typically seen in the URL bar of your browser, first create an image using the gimp. Save the file as "favicon.pnm" or "favicon.ppm" with raw encoding.
Now you will use ppmtowinicon from the netpbm-tools package to convert it:
$ ppmtowinicon -output favicon.ico favicon.pnm
or
$ ppmtowinicon -output favicon.ico favicon.ppm
You will want to place the favicon.ico in the DocumentRoot of your website(s).