https://github.com/kenjis/codeigniter-tettei-apps/blob/d930eecac9d4308317826a5980966ab8ecbb5c17/application/controllers/Bbs.php#L278 - 一度生成されたキャプチャデータは2時間有効 - 全ユーザ共通
codeigniter-tettei-apps/application/controllers/Bbs.php
Line 278 in d930eec