save image to custom meta box

1function save_joe_details($post_id){
2  global $post;
3  if ( defined('DOING_AUTOSAVE') && DOING_AUTOSAVE )
4  return $post_id;
5  update_post_meta($post->ID, "custom_field_image", $_POST["custom_field_image"] );
6}
7add_action('save_post', 'save_joe_details');
8