Now cleans itself up after conversion.

mkfavicon.sh

#!/bin/sh

# originally from
# http://bergamini.org/computers/creating-favicon.ico-icon-files-with-imagemagick-convert.html

input=$1
working=`mktemp -d -t mkfavicon-XXXX`

convert $1 -resize 256x256 -filter Gaussian -transparent white ${working}/favicon-256.png
convert ${working}/favicon-256.png -filter Gaussian -resize 16x16 ${working}/favicon-16.png
convert ${working}/favicon-256.png -filter Gaussian -resize 32x32 ${working}/favicon-32.png
convert ${working}/favicon-256.png -filter Gaussian -resize 64x64 ${working}/favicon-64.png
convert ${working}/favicon-256.png -filter Gaussian -resize 128x128 ${working}/favicon-128.png
convert ${working}/favicon-16.png ${working}/favicon-32.png ${working}/favicon-64.png ${working}/favicon-128.png ${working}/favicon-256.png -colors 256 favicon.ico

rm -r ${working}

echo "Image file ${input} successfully converted to favicon.ico."