你不需要使用get_posts( \'post_type=attachment\' ) 要返回附件ID？比如：

$args = array( 
     \'post_type\' => \'attachment\', 
     \'numberposts\' => -1, 
     \'post_status\' => null, 
     \'post_parent\' => $post->ID 
);    
$attachments = get_posts( $args );
$myimageid = $attachments[0]->ID;

wp_get_attachment_image( $myimageid, \'full\' );