One of the limitations in Winos 8 was that we could not set our desired wallpaper/background to the new start screen. Instead we had to select with some images/designs Microsoft has provided by default.
With the release of Windows 8.1, Microsoft has included an option where we can have our desktop wallpaper as the start screen background. To enable this option there are 2 methods
1) Right click on the task bar and select properties
2) In the properties Taskbar and Navigation properties window, click the navigation tab and check the “Show my desktop background on Start” option and click OK
1) On the start screen charms bar, select the settings charm
2) Click Personalize
3) Select the wallpaper