Thanks for the series! Having real-world homework helps me hone my skills better. Once I knew what you were going for, I coded it up a little differently. I went for variables to represent the important offsets in the window and image, then did simple comparisons between them. Seemed more readable to me.
Great exercise. I personally don't like the feature of removing the active class when the user scrolled past the image, so I did not include it in my solution. But, to each their own.