I wanted to update the icon of this blog (to become what else? a cat) and I didn’t remember how I had created the previous one but I do remember I did it via GIMP.
This time though, I found a pretty simple imagemagick command and it worked like a charm.
convert <your-image-here> -define icon:auto-resize=256,64,48,32,16 favicon.ico
Here are all the available options for the imagemagick