How to add the custom background functionality support to wordpress theme

In new wordpress version we can add the background image or color to wordpress websites. Many older wp themes has no support for custom background functionality.
You can very easily add the custom background support to your wordpress theme. You just need to copy following code and put in your functions.php file.

Image may be NSFW.
Clik here to view.

add_filter( 'body_class', 'wpapi_body_class' );
function wpapi_body_class( $classes ) {
	$background_color = get_background_color();
	$background_image = get_background_image();

	if ( empty( $background_image ) ) {
		if ( empty( $background_color ) )
			$classes[] = 'custom-background-empty';
		elseif ( in_array( $background_color, array( 'fff', 'ffffff' ) ) )
			$classes[] = 'custom-background-white';
	}


	return $classes;
}


// Activate custom background and set callback function
if ( function_exists( 'add_theme_support' ) ) {
    $defaults = array(
    'default-color' => '000000',
    'default-image' => get_template_directory_uri() . '/img/background.png',
    'wp-head-callback' => 'my_theme_background_cb',
    'admin-head-callback'    => '',
    'admin-preview-callback' => ''
    );
    add_theme_support( 'custom-background', $defaults );
}