OK I wrote a little bit of javascript to populate the Meta og:image with the featured image of my choice. It's a one-time hack you add to your header file.
In my wordpress post, I add the id "featured-image" (I know with later wordpress this is built-in, I'm on an old one).
<xmp><img src="http://mysite.com/catphoto.jpg" id="featured-image" /></xmp>
I write a meta tag for the og:image with a placeholder, such as my blog log. Add "id="meta-image" to the tag, i.e.
<meta property="og:image" src="http://mysite.com/logo.jpg" id="meta-image" />
Then add this javascript in the header:
<script type="text/javascript" src="http://code.jquery.com/jquery-1.7.1.min.js"> </script>
<script type="text/javascript">
$(document).ready( function(){
var featured_image = $("#featured-image").attr("src");
$('meta[property="og:image"]').attr("content",featured_image);
});