Darkness
Welles pans the camera down from the funeral procession at the opening of the film into darkness, and from darkness we are taken into water reflecting a castle. The imagery shows us that we are being taken into the past as we know that Othello and Desdemona are dead. Now we will be shown what happened and the imagery tells us this.
Iago and Roderigo
We see Iago and Roderigo following following Othello and Desdemona as they make their way from the chapel to his bedroom. Their looming unseen by the lovers shows us that they are plotting against the pair, and what they do is done in the shadows, undetected by Othello and Desdemona.
Darkness in the Light
We see Iago wearing a dark cloak in the street out front of Brabantio's home. As the sunlight shines through, it appears Iago to be the only darkness amid the light. The imagery tells us that he is a man who is full of deception and is bringing darkness upon what should be a joyful union.
Storm
We see the sea waves crashing against the city walls and the lightning strikes in the sky. The imagery relates to the impending storm that will be within Othello, and will bring down the great General because of the deception and betrayal of Iago.
