Image not showing up in media loader success area – followup

untested, but it should work theoretically:

add_filter('get_attached_file', function($path, $file, $attachment_id){

  // get the post object of the current attachment
  $att = get_post($attachment_id);

  // prepend attachment post parent ID to the file name
  return substr_replace($path, "{$att->post_parent}/{$file}", -strlen($file));
});

---

Another filter, attempts to “fix” the path returned by WP’s upload handler:

add_filter('wp_handle_upload', function($results){
  global $post;

  if(empty($post))
    return $results;

  extract($results);

  $uploads = wp_upload_dir();

  $file = str_replace($uploads['basedir'], "{$uploads['basedir']}/{$post->ID}", $file);
  $url = str_replace($uploads['baseurl'], "{$uploads['baseurl']}/{$post->ID}", $url);

  return compact('file', 'url', 'type');
});

This will not work if the media uploader doesn’t expose the current post inside the global $post variable.