Most artwork, with the exception of sculpture, is two dimensional, let's face it. We're not talking crafts, now, (though crafts is another of my big loves). Let's talk murals.
Murals are, for the most part, huge, and hugely two-dimensional. They can be indoors or outdoors. They can be painted on with a brush or with spray paint. They can have subjects that are realistic, or decorative, or abstract. Some murals are historic in theme, some seem to be dream-like fantasies (Maxfield Parrish), some are incredible in size and stature (Michaelangelo). They can be advertisements. They can incorporate lettering or calligraphy, or they can consist entirely of such lettering.
If it is an outdoor mural, the artist would want to use non-fading outdoor paint. If it is an indoor mural the artist might want to use non-smelly types of paint!
But in any case only paint is used; no glue-ons, no paste-ons, and nothing that will not last. A mural is meant to "last forever," no matter to what kind of lighting or weather (or kids!) it is exposed.