我认为你不能用get_the_post_thumbnail 函数获取上次上载的媒体，但您可以使用get_post 获取最新附件，然后wp_get_attachment_image 显示图像。

$attachments = get_posts( array(
    \'post_type\' => \'attachment\',
    \'posts_per_page\' => 1,
    \'post_status\' => null,
    \'post_mime_type\' => \'image\'
) );

foreach ( $attachments as $attachment ) {
    echo wp_get_attachment_image( $attachment->ID, \'thumbnail\' );
}