This post is an extension of the above post & solution to baben's(blog mate) query which empowers your readers to change background image of your blog with the click.
You can add this widget to your blog by making certain minor modifications to the code.
Best use of this could be to change the background image of the footer which can be doen with few modifications
Lets first see an example :Click below image to change background image
You can add background images or change this sample, only replace the URL of the image (it is twice) for yours.
The URL of the image sets twice where indicated, the first is to be applied as wallpaper and the second is an example for the reader to click.