I regularly have to look up the ImageMagick syntax for converting image files to ico formats when I’m creating a favicon.ico
The convert
command, part of the ImageMagick suite, is quite helpful and versatile.
Here is the basic command to create a multi-size favicon.ico file from a png, jpeg, or other image:
convert source.png -define icon:auto-resize=256,128,64,48,32,24,16 favicon.ico