"The balance of the frame—the way an actor is relating to the space in the frame—is the most important factor in helping the audience feel what the character is thinking.” Roger Deakins
Brief Encounter (David Lean)
The devastating, gut-twisting Dutch moment is the one that I considered first, followed closely by the final scene, by any number of the night-time silhouettes, and any/all of the train images. But I went with this one, finally, because it's so instantly arresting. And because it encapsulates the mixture of happiness and apprehension that fills Laura throughout the entire story. (Also, is it just me, or does the reflection seem to have a different emotion than she does in this particular shot?)
Stalker (Andrei Tarkovsky)
Another film that demands an almost-absurd amount of discipline from anyone trying to come up with a single frame, since nearly every frame is deserving of copious attention. The last few moments seem like the obvious answer, at first (except SPOILERS!), or something from the Tunnel or the Room or the Zone itself. Or something from the moody, contrasty opening scenes and the mirror moments that follow upon their return. Or the terrifying glimpse of Tarkovsky's post-visit Earth. But always, I return to this one. It’s so unsettling, and the incomprehensible look in his eyes gets me every time.
Hero (Zhang Yimou)
Picking a single, representative image from this visual masterpiece is nearly impossible. There are so many options to choose from, and all of them are correct—the lake fight, the falling leaves, the Emperor's bodyguards recoiling from Nameless in fear, the homage to Kurosawa's Throne of Blood, the spoiler-y final shot—but the focus decision Yimou makes in this frame is just perfect. (Click to enlarge. Please.)