When we pick up a camera, and frame our shot, we are either consciously or subconsciously doing one of two things. We are either trying to record information (a pin sharp image, recording exact details), or we are trying to record ‘happenings’, images that depict or portray movement or events. The latter can be shot in two ways. Either (again) pin sharp but with the subject matter suggesting movement (a sprinter caught mid stride), or by the use of a slower shutter speed which will cause the effect of motion blur.
Robert Frank understands this and is able to take it a step further to increase the ‘content’ of his work. In Elevator Girl

Frank, Robert. 1955, Elevator Girl, The Americans. Philadelphia Museum of Art
Frank is able to make use of recording both blur and sharp imagery in one picture. This dichotomy serves to create focus and tension within the image. In this single image Frank has captured a specific ‘moment in time’ that can never be recaptured, and framed it within directional movement prompting so many questions and stories within stories. The person in the centre of the frame is clearly the main subject matter, with her pose suggesting many questions and an air of vulnerability. The figures either side of her clearly frame her but are all blurred. The suggestion is that there are two ladies leaving the elevator and are oblivious to what they are leaving behind. The figure on the right is also blurred through motion and is also in silhouette. Combined with the apparent direction of his gaze, this makes him a very sinister figure, and suggests that there is danger for the now helpless ‘victim’. Had the image been in sharp throughout, then the character on the right may not have had quite the same air of menace, and it may have shown his intentions to be other than previously described.