How to add background image control to page admin controls?

It can be done with a custom field and the CSS should be changed to .php file:

$image = get_post_meta( $post->ID, "ImagePathFromCustomField", true );
if ( $image != '' ) { 
    ?>
    <style type="text/css">
        .bg-image { 
            background-image: url(<?php echo $image; ?>); 
            background-repeat: repeat; 
        }
    </style>
    <?php
}