Picking up on the conversation from this post, I want to talk about what widescreen key art gets you in today's digital age.
So we have two forms of key art these days that are being seen by audiences:
You must stop and nod your head up and down to get the full impact of the artwork. It is not designed to fill people's field of view if said person is walking by.
2) Then we have the variation on this which I like to call "widescreen key art" , but could just as easily be called "wallpaper" (a nod to digital) or "Billboard" ( a nod to very effectively placed and formatted advertising). Two examples are below:
Notice how they fill your view?
If you were to walk by this on the street or in the theater it would more likely catch your eye because of the duration of its occupation of your field of vision.
And damn if (subconsciously at least) it doesn't mean "this is a big movie."
Even if you are going to watch that movie on a screen that's this small:
Filling the frame with interesting stuff for the audience to focus on:
Story, color, movement , texture, momentum...
and make sure that frame fills their field of view.
Hey! It works for billboards...
Edit to Add: I am just now recalling something my pulp web bastard Chris Sharpe said to me: "When people look at a 3-D rendering of a book they are more likely to buy off the website." Consider widescreen key art to be the equivalent to 3D book art. Wider view that seems epic and real.