Facebook open graph snippet to set default image

Adding this snippet to the functions.php of your wordpress theme will allow you to specify Facebook Open Graph information on your WordPress posts. Allowing you to specify which image should be displayed when sharing your article on Facebook among other things.

function diww_facebook_image() {
                echo '<meta property="fb:admins" content="ADMIN_ID" />';
                echo '<meta property="og:title" content="' . get_the_title() . '" />';
                echo '<meta property="og:site_name" content="' . get_bloginfo('name') . '" />';
        global $post;
        if ( is_singular() ) { // only if a single post or page
                echo '<meta property="og:type" content="article" />';
                echo '<meta property="og:url" content="' . get_permalink() . '" />';
        if (has_post_thumbnail( $post->ID )) { // use featured image if there is one
                $feat_image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'large' );
                echo '<meta property="og:image" content="' . esc_attr( $feat_image[0] ) . '" />';
         }else{ // use site logo in case no featured image
                echo '<meta property="og:image" content="http://yourdomain.com/logo.png" />';
         }
        }
        if ( is_home() ) { // for homepage only
                echo '<meta property="og:type" content="website" />';
                echo '<meta property="og:url" content="' . get_bloginfo('url') . '" />';
                echo '<meta property="og:image" content="http://yourdomain.com/logo.png" />';
        }
}
add_action( 'wp_head', 'diww_facebook_image' );