How does Facebook Sharer select Images and other metadata when sharing my URL?

Question

When using Facebook Sharer, Facebook will offer the user the option of using 1 of a few images pulled from the source as a preview for their link. How are these images selec

Answer 1

Put the following tag in the head:

From http://www.facebook.com/share_partners.php

As far as what it chooses as the default in the absence of this tag, I'm not sure.