Create a favicon from a png image.

image-magick-favicon.sh

# ImageMagick command to create a favicon from image.png
convert image.png  -bordercolor white -border 0 \
          \( -clone 0 -resize 16x16 \) \
          \( -clone 0 -resize 32x32 \) \
          \( -clone 0 -resize 48x48 \) \
          \( -clone 0 -resize 64x64 \) \
          -delete 0 -alpha off -colors 256 favicon.ico
          
# Transparent background
convert favicon.png \                                               ok
          \( -clone 0 -resize 16x16 \) \
          \( -clone 0 -resize 32x32 \) \
          \( -clone 0 -resize 48x48 \) \
          \( -clone 0 -resize 64x64 \) \
          -delete 0 -colors 256 favicon.ico

Source: https://www.imagemagick.org/Usage/thumbnails/#favicon