When I'm posting a link for a WordPress page or post on a Facebook Page wall (using the "Post a link" option), I want Facebook to offer up, as choices, (a) all images which are embedded in the linked page/post as well as (b) a set of default images (in case the page/post in question has no embedded images).
What I've done is add (to wp_head) several candidate images in separate link rel="img_src" tags.
The problem is that these link rel tags appear to override any images that are actually embedded in the page/post.
Any advice would be appreciated.