Trouble with leverage browser caching and specifying a cache validator

This plugin works well, except there is one problem. It caches all the images, js, css and etc fine, but it has a problem with caching these .jpg images. They are thumbnails from youtube, like this for example, http://img.youtube.com/vi/018PqeeJgV0/0.jpg. I added ExpiresByType image/jpg "access plus 1 month", but it did not work. Is it because it’s from youtube? Any help would be appreciated!

Regards,
Alex

http://ww.wp.xz.cn/plugins/w3-total-cache/