When adding the Facebook Like button to a page, be sure to add the image Property meta tag:

<meta property=”og:image” content=”<full path to image>”/>

Here are other tag that can be added:

<meta property=”og:title” content=”<Title of the page>”/>

<meta property=”og:site_name” content=”<Title of the site>”/>

Here is the Facebook Like button generator:

http://developers.facebook.com/docs/reference/plugins/like/