Robert Frank often showed images like this that were controversial. Many of his well known images showed unfavorable areas of American lifestyle or habits. With his pattern of dampening reputation I feel like he may be trying to convey a similar message in this photograph.
This picture shows London, England as a dim and macabre place. The main subject is a man wearing a jet black suit and is focused and contrasted nicely. The rest of the image is dull and hazy but it enhances the man the closest man to the subject has bad posture, he is leaning his head forwards a little with his collar up, this helps enhance the main subjects posture. It almost seems like he is fearlessly charging because his arms are folded behind him, exposing his frontside to the haze and uncertainty the London fog emits. He could also be seen with a relaxed or comfortable posture heading into a dark era with a positive feeling.