Facebook open graph snippet to set default image

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' );