The first was taken on November 4, 1963. It's one week after Dylan's first performance outside the Village, where he first sang "The Times They Are A-Changin'" in front of an audience. The location is 132nd St, with the Harlem River and the Park Avenue (Metro North) railroad bridge in the background.
Bob Dylan, Musician, 132nd and FDR Drive, Harlem, New York, November 4, 1963
The pose is casual, the slightly upturned face and barest hint of a Mona Lisa smile show an openness of character. He's wearing a flannel shirt, blue jeans, and workingman's boots. There's a pen in his pocket. The guitar case is beaten up, the background is industrial, literally gritty. He looks young, but not naive; open to experience, and ready to meet it. The clothes, location, beat-up guitar case are all markers of his background. He could be just in from Minnesota.
The second was taken just sixteen months later. It was between the finished production and the release of Bringing It All Back Home, his first record that included a rock band on some tracks. There are of course a lot of differences, but first I want to point out the similarity of pose: Hands in pockets, right knee slightly bent, weight on left foot.
Bob Dylan, Musician, Central Park, New York, February 10, 1965
The first difference I noticed was the clothes. They're no longer working man's clothes. The boots are pointy-toed, the pants straight leg. He's wearing a suede coat. There's no sign of a pen or guitar. And of course there's the difference in location, striking even if you know little or nothing about the socioeconomic geography of New York. The overall picture is much darker, and the light is behind Dylan, not above him.
Here, the gaze is more direct. The angle of the head and the light cast the eyes in shadow, making them look hooded, guarded. The eyes are slightly heavier, and the lips, barely turned up in the first photo, are now barely turned down. "The Times They Are A-Changin'" has become the anthem of his generation. Instead of looking openly to the future, he's practically glaring at it. He bears the weight of his experience in the intervening months, and he knows a lot more is coming.
This shows how much you can see in just the surface of a good portrait. I think the very slight difference in poses say a lot about the large difference in Dylan's life and status between one photo and the next.
(A brief note: I've been looking at the pictures in the book, which are very large and well reproduced.)