This is a small module that uses TheExtensionLab_MegaMenu's 'theextensionlab_megamenu/extra_attributes' config node and the new event menu_get_category_menu_data_after, to add a new category attribute 'icon_image' to the Menu Object for use on the frontend.
NOTE: Since most would do this as a theme customisation the frontend updates are not included but you can see more information in the blog post below.
ALSO NOTE: Depends on TheExtensionLab_MegaMenu