The marquee or header image is designed as a background accent for your course. Exercise caution when using logos or text, as it may not be visible to all users on all screen sizes.
Marquee images will dynamically re-size depending upon the screen size and will appear differently to most of your members, depending upon the device they are using, as well as screen settings.
The image will resize from the center of the image, so make sure the area you want as your main focal point is in the center. There is not a way to make this image static as it wouldn't provide a good viewing experience under most circumstances.