Adds Facebook Graph meta tags to Wordpress blog pages and thumbnail support to your Wordpress theme

functions.php

<?php

if ( function_exists( 'add_theme_support' ) ) {
  add_theme_support( 'post-thumbnails' );
}

function the_facebook_graph_data() {
  // setup the default site attributes
  $graph;
  $graph["site_name"] = "YOUR_SITE_NAME";
  $graph["admins"] = "YOUR_FACEBOOK_ID";
  $graph["app_id"] = "YOUR_APP_ID";
  // setup the default page attributes
  $graph["type"] = "blog";
  $graph["title"] = "DEFAULT_TITLE";
  $graph["image"] = "LINK_TO_DEFAULT_BLOG_IMAGE";
  $graph["description"] = "YOUR_WEBSITE_DESCRIPTION";
  $graph["url"] = "YOUR_WEBSITE_URL";
  // override the page attributes for individual posts
  global $post;
  $postid = $post->ID;
  if(is_single()) {
    $graph["type"] = "article";
    $graph["title"] = $post->post_title;
    // Image (thumbnail)
    if(has_post_thumbnail($postid)) {
      $image = wp_get_attachment_image_src(
        get_post_thumbnail_id($postid),'post-thumbnail', false);
      $graph["image"] = $image[0];
    }
    // Description (excerpt)
    $excerpt;
    if($post->post_excerpt) {
      $excerpt = strip_tags($post->post_excerpt);
    } else {
      $excerpt = strip_tags($post->post_content);
    }
    $excerpt = str_replace(array("\n", "\r", "\t"), ' ', $excerpt);
    $graph["description"] = substr($excerpt, 0, 125);
    // URL (permalink)
    $graph["url"] = get_permalink($postid);
  }
  foreach($graph as $key => $value) {
    echo '<meta property="og:' . $key . '" content="' . $value . '" />';
  }
}
add_action('wp_head', 'the_facebook_graph_data');

?>