With CyberSEO you can do it as easy as this:
- go to CyberSEO->Tools;
- insert the following code into the "PHP Code <?php .. ?>" box:
Code:
$thumb = get_post_meta($post->ID, "YOUR_THUMBNAIL_CUSTOM_FIELD_NAME", true);
cseo_attach_post_thumbnail($post->ID, $thumb, $post->post_title);
- click "Apply These Modifications To All Existing Posts".
