Maybe you heard about the Opengraph Tags used by Facebook ? Basically “including Open Graph tags on your Web page, makes your page equivalent to a Facebook Page”:
http://developers.facebook.com/docs/opengraph/
And yes, you’ll get a nice like Thumbnail of your web page using this stuff (knowing that the share function is now deprecated: http://developers.facebook.com/docs/share/ and has been replaced with like).
This is a quick code for WordPress (minimal tags), just adapt, then copy & paste to your wordpress theme header:


