Cacher is the code snippet organizer for pro developers

add_action('do_meta_boxes', 'replace_featured_image_box');  
function replace_featured_image_box()  
{  
    remove_meta_box( 'postimagediv', 'page', 'side' );  
    add_meta_box('postimagediv', __('Page Background Image'), 'post_thumbnail_meta_box', 'page', 'side', 'low');  
} 

add_filter( 'admin_post_thumbnail_html', 'add_featured_image_instruction');
function add_featured_image_instruction( $content ) {
    return $content .= '<p>The Featured Image is an image that is chosen as the representative image for Posts or Pages. Click the link above to add or change the image for this post. </p>';
}