如果您使用save_post 钩子，每次发布或更新内容时，都会刷新特色图像。注意：确保ACF设置为返回图像ID，这不是其默认值。

add_action( \'save_post\', \'wpse_set_featured_image\' );
function wpse_set_featured_image($post_id) {
    // get author id
    $author_id = get_the_author_id($post_id);
    // get author\'s image
    $author_image_id = get_user_meta($author_id, \'your_acf_img_var_name\', true);
    // fallback image
    if(empty($author_image_id)) {
        // set to an existing image ID to use as a fallback
        $author_image_id = \'4\';
    }
    // at last, set the post featured image
    set_post_thumbnail($post_id, $author_image_id);
}