Windows 8 Metro mode won’t allow you to choose your own background image. This is not surprising at all since we are used to it from Windows Phone design style. According to an interview with Tech Radar, Windows 8 director of communications Chris Flores pointed out that
“Not only would a photo not stretch and scale as you add more tiles and groups and zoom in and out of the Start screen, it would also be covered up so much by the tiles that you’d never see it.”
But Windows 8 will provide a theme picker page as seen in the image above where you can choose between 8 different styles and colors. Improving from the developer preview, Windows 8 now includes more options to navigate and use Metro mode using mouse and key board. One such example is the new semantic zoom option which will allow you to move or rename groups of tiles. You can now activate semantic zoom mode by clicking an icon at the bottom right corner.
You can read more about the changes and improvements here at TechRadar.