So transparent and white are different. If you really want a transparent background you can crop the image and cut it to a larger image, then save it as a GIF file with a transparent background. A white background can be done the same way, but saving it as a JPG file (for example) will force the background to a color (usually white by default) because it doesnt support the transparent background.

When I scan an image I do as Greg suggested and it ends up with a white background.