We currently have a PHP script doing this, but it fails constantly, so I'm looking for a solution in Ruby. Basically we are collecting favicons and need to convert any that are in the .ico format into a .png format.
Please do not provide links to any hosted services to do this... we've probably already tried them all and abandoned them (this includes Google and Yahoo) ;)
Use ImageMagick or GraphicsMagick, both available as PHP modules (and very similar); in Ruby use the RMagick interface.