When playing back an old Hercule Poirot episode which was filmed in 4:3 resolution I crop the image for removing the black bars on left and right sides:
The image itself is 768x576. (There is no window left border because I align the side of the image to the side of my screen)
But if I take a screenshot using Shift+S then the resulting 768x576 image is taken from the non visible left black bar so the final image is missing the right part: