ファイル構成だけなんとかした（中身はまだ）．

modules/delete.php

@@ -0,0 +1,38 @@
+<?php
+require "${_SERVER['DOCUMENT_ROOT']}/database.php";
+
+
+$mysqli = set_mysql ('miteruzo_bbs');
+
+$mysqli -> set_charset ('utf8');
+
+$thread = $_GET['thread'];
+$id = $_GET['id'];
+$pass = $_GET['pass'];
+
+if ($result = $mysqli -> query ("
+        SELECT
+          pass, image
+        FROM
+          responses
+        WHERE
+          (thread_id = {$_GET['thread']}) AND (response_id = {$_GET['id']})")):
+    $row = $result -> fetch_assoc ();
+
+    if ($_GET['pass'] == $row['pass']):
+        $mysqli -> query ("
+                UPDATE
+                  responses
+                SET
+                  deleted = 1
+                WHERE
+                  (thread_id = $thread) AND (response_id = $id)");
+
+        echo "消しましたぁ!!<br /><br /><img style='border: solid 1px' src='image/{$row['image']}' />";
+    else:
+        echo '残念．<br />削除用パスワードが違います．';
+    endif;
+
+    echo "<br /><br />5 秒後に元のページに戻ります．<br /><br /><a href='./?thread=$thread#$id'>戻らない場合はこちら</a><script>setTimeout (function () {window.location.href = `./?thread=$thread#$id`}, 5000)</script>";
+endif;
+