Windows does not natively allow you to do this as far as I know.
But there is an easy alternative.
Open the image in any image editor. Increase the image to the resolution of your monitor, but don't resize the image itself. Now you can color the remaining of the background to your liking, including white.
Save the image, and set the new image as your background.
You can even decide to combine multiple images to one image if you want more of a background.