WordPress Multiple Post Thumbnails plugin setup. Example of setting up a background image option.

multiple-post-thumbnails.php

/**
 * Multiple Post Thumbnails (plugin compatibility)
 * http://wordpress.org/extend/plugins/multiple-post-thumbnails/
 */
if ( class_exists( 'MultiPostThumbnails' ) ) {
  $types = array( 'page' );
	foreach ( $types as $type ) {
		new MultiPostThumbnails( array(
			'label'     => _x( 'Background Image', 'admin', 'mytheme' ),
			'id'        => 'background-image',
			'post_type' => $type
		) );
	}
}