sharing a link on facebook: how to get thumbnails?

I've put in my page's header the following

<link rel="image_src" href="http://fractalsoft.s3.amazonaws.com/sfondo.jp2" />

but the thumb is not showing up.

I think the problem is that the image is located outside the开发者_高级运维 site.

Is there a way to solve this?

Thanks!

---

Ok, i just added this inside my tag and i was done:

<meta property="og:image" content="http://s3.amazonaws.com/andrea/photos/activities/26/medium.jpg?1304082168"/>

And there are other useful tags:

    <meta property="og:title" content="..."/>
    <meta property="fb:app_id" content="..."/>
    <meta property="og:type" content="activity"/>
    <meta property="og:url" content="..."/>
    <meta property="og:image" content="..."/>
    <meta property="og:site_name" content="..."/>
    <meta property="og:description" content="..."/>

Hope this helps!