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

As of 2013, if you're using facebook.com/sharer.php (PHP) you can simply make any button/link like:

share on facebook

Link query parameters:

p[title] = Define a page title
p[summary] = An URL description, most likely describing the contents of the page
p[url] = The absolute URL for the page you're sharing 
p[images][0] = The URL of the thumbnail image to be used as post thumbnail on facebook

It's plain simple: you do not need any js or other settings. Is just an HTML raw link. Style the A tag in any way you want to.