您可以这样尝试：

if ( has_post_thumbnail() ) { // check if the post has a Post Thumbnail assigned to it.
        the_post_thumbnail( \'full\', array( \'class\'  => \'responsive-class\' ) ); // show featured image
    } 

post_thumbnail_html

From Codex:

apply_filters( \'post_thumbnail_html\', string $html, int $post_id, string $post_thumbnail_id, string|array $size, string $attr )

此筛选器由调用get_the_post_thumbnail位于post\\u thumbnail\\u template的第177行。php之后$html 已设置为：

$html = wp_get_attachment_image( $post_thumbnail_id, $size, false, $attr );

在上下文中筛选：

/**
* Filters the post thumbnail HTML.
     * @param string       $html              The post thumbnail HTML.
     * @param int          $post_id           The post ID.
     * @param string       $post_thumbnail_id The post thumbnail ID.
     * @param string|array $size              The post thumbnail size. Image size or array of width and height values (in that order). Default \'post-thumbnail\'.
     * @param string       $attr              Query string of attributes.
*/
return

 apply_filters( \'post_thumbnail_html\', $html, $post->ID, $post_thumbnail_id, $size, $attr );

添加data-featherlight="mylightbox" 示例：

add_filter(\'post_thumbnail_html\', \'my_thumbnail_filter_method\', 10, 5 );
function my_thumbnail_filter_method($html, $post->ID, $post_thumbnail_id, $size, $attr) {
     $id = get_post_thumbnail_id();
     $src = wp_get_attachment_image_src($id, $size); 
     $alt = get_the_title($id); /
     $class = $attr[\'class\'];

    $html = \'<img src="\' . $src[0] . \'" alt="\' . $alt . \'" class="\' . $class . \'" data-featherlight="mylightbox" />\';
}

1. begin_fetch_post_thumbnail_html
2. end_fetch_post_thumbnail_html$post->ID, $post_thumbnail_id, $size. 看起来像是过滤post_thumbnail_html 是访问<img> html字符串。

   上的注释has_post_thumbnail(), 因为它似乎经常出现：如果有任何图像附加到帖子，此方法将返回true，而不是专门针对帖子缩略图（又名特色图像）。