//评论添加验证码
function spam_protection_math(){
	$num1=rand(0,9);
	$num2=rand(0,9);
	echo "<label for="math">请输入 <i>$num1 + $num2 = ?</i> 的计算结果：</label>n";
	echo "<input type="text" name="sum" class="text" value="" size="25" tabindex="4">n";
	echo "<input type="hidden" name="num1" value="$num1">n";
	echo "<input type="hidden" name="num2" value="$num2">";
}
function spam_protection_pre($commentdata){
	$sum=$_POST['sum'];
	switch($sum){
		case $_POST['num1']+$_POST['num2']:
		break;
		case null:
		wp_die('对不起: 请输入验证码。<a href="javascript:history.back(-1)">返回上一页</a>','评论失败');
		break;
		default:
		wp_die('对不起: 验证码错误，请<a href="javascript:history.back(-1)">返回</a>重试。','评论失败');
	}
	return $commentdata;
}
if($comment_data['comment_type']==''){
	add_filter('preprocess_comment','spam_protection_pre');
}

<?php spam_protection_math();?>