Of course, if you want to choose one of your own photographs, pictures or an image you find on a website as your background, find the image and right-click on its icon. Choose "Set image as desktop background" and it will become your new theme. To save it as a theme for future use, open the Personalize option again and click "Save theme." Now you can reuse it again and again without having to hunt for the original image. Once you have settled on your theme, click on the Desktop Background option at the bottom of the Personalize window. Here you can see all the images within a particular theme and tick or untick them, removing unwanted ones from your cycle of images. You can also choose how the picture is shown on-screen, although leaving it in Fill mode will be fine unless you start using odd-shaped images. There is also a Shuffle tick box, allowing you to muddle up the order of the chosen images, so you won't know what is coming next.