"There are different rules for commercials and freebees?" The rules aren't different, the level of tolerance is. "Can I in a picture have a gigantic Coca-Cola logo as in the bladruner?" Yes. Be sure to accurately note that the trademark in use belongs to the coca-cola corporation. "Can I make fanart with charters from Star trek, or an anime?" Yes. However, your ability to display and distribute that fan art may be limited according to the needs and perspectives of the owners of the trademarks and copyrights concerned.

thou and I, my friend, can, in the most flunkey world, make, each of us, one non-flunkey, one hero, if we like: that will be two heroes to begin with. (Carlyle)