With Linux / Ubuntu / Whatyouwant here is the process to generate a favicon (found on linuxproblem.org) :

Your problem

You want to create an icon for your website (which is displayed in the browser’s location bar). You already know, that you have to place a file called favicon.ico in your web server’s document root directory. But how can you create one?

The solution

You need an image file that GIMP can open (PNG, GIF, etc.). And you need the command line tool ppmtowinicon from the netpbm-tools (on SuSE you have to have installed the package netpbm). Now perform the following actions:
# Open your image with GIMP.
# If your image is not a square then resize the canvas with GIMP.
# Scale the image to 16×16 pixel (Image, Scale image).
# Choose File, save as.. and save as favicon.pnm or favicon.ppm with raw encoding.
# Close GIMP
# Convert favicon.pnm resp. favicon.ppm using the command line utility ppmtowinicon:

> ppmtowinicon -output favicon.ico favicon.pnm

resp.

> ppmtowinicon -output favicon.ico favicon.ppm

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