Um "key art" pode ser sinónimo de poster.
Veja na Wiki:
http://en.wikipedia.org/wiki/Film_posterThe annual Key Art Awards, sponsored by The Hollywood Reporter, include awards for best film poster in the categories of comedy, drama, action adventure, teaser, and international film. The Hollywood Reporter defines the term "key art" as "the singular, iconographic image that is the foundation upon which a movie's marketing campaign is built.
Se se trata de algum material informativo publicitário, "cartaz" ou "poster" podem aplicar-se, talvez dependendo da sua dimensão.