<!-- OGP -->
<?php if (is_single() || is_page()) { ?>
<?php while (have_posts()) : the_post(); ?>
<meta property="og:title" content="<?php the_title(); ?>" />
<meta property="og:type" content="article" />
<?php if (get_post_meta($post->ID,'カスタムフィールド名',true)): ?>
<meta property="og:image" content="<?php
$fileid = get_post_meta($post->ID, カスタムフィールド名, false);
$file = wp_get_attachment_image_src($fileid[0], 'full');
echo $file[0];
 ?>" />
<?php elseif (has_post_thumbnail()): ?>
<?php
$image_id = get_post_thumbnail_id();
$image_url = wp_get_attachment_image_src($image_id, $size = 'thumbnail');
?>
<meta property="og:image" content="<?php echo $image_url[0]; ?>" />
<?php else: ?>
<meta property="og:image" content="任意の画像URL" />
<?php endif; ?>
<meta property="og:url" content="<?php the_permalink(); ?>" />
<?php endwhile; ?>

<?php } elseif (is_home()) { ?>
<meta property="og:title" content="<?php bloginfo('name'); ?>" />
<meta property="og:type" content="blog" />
<meta property="og:image" content="任意の画像URL" />
<meta property="og:url" content="<?php bloginfo('url'); ?>" />
<meta property="og:description" content="<?php bloginfo('description'); ?>" />
<?php } else { ?>
<meta property="og:title" content="<?php wp_title('|', true, 'right'); ?><?php bloginfo('name'); ?>" />
<meta property="og:type" content="article" />
<meta property="og:image" content="任意の画像URL" />
<meta property="og:url" content="<?php echo get_bloginfo('url').$_SERVER['REQUEST_URI']; ?>" />
<meta property="og:description" content="<?php bloginfo('description'); ?>" />
<?php } ?>
<!-- /OGP -->

OGP

OGP画像シミュレータ