the image is compiled into a base64 line of text at the start of icons.mod.gml. i added this part a few months after i made the skins and had developed a habit of doing images like this (easier to download, harder to edit). you can find image_to_base64/base64_to_image converters online
i think this is the latest image i used (you have to change the amount of frames the game reads from this if you change it)