If you have the Professional Version of Question Writer you can add your own background image or piece of Flash in place of the one from the theme. See also Background Image.
Use this option to adjust the quality of any jpg images used. Set the size/image quality balance to suit your own quizzes. If your quiz is designed for use on a CDROM - usually you'll want to have high quality images and a large file size. If the quiz is to be available over the internet you'll often want a lower quality image and a smaller file size to minimize quiz download times.
You can choose which version of Flash your images will be saved and published as - by selecting from the drop down box. The higher the version number that you select, the better the image quality will be.