To add images that serve as design elements (and not content), put them in src/img folder. This folder will be automatically copied to the project destination directory (usually web) when running npm build tasks.
To add new icons, put them in src/img/icons directory. They need to be in SVG format and have no extraneous white space around. For usage refer to iconography section of Guidelines.
Use RealFaviconGenerator to generate the favicon suite, copy them to src/favicon folder and make sure the paths are present in the <head> tag as instructed.