首先用session將隨機生成的驗證碼的值傳到頁面，然后獲取當前文本框中輸入的值 ?進行對比；代碼如下：

?

生成的隨機數，把它傳到session里面

<?

session_start(); ? 必須要先打開session開關。
$s = array("a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z","0","1","2","3","4","5","6","7","8","9");
$r="";

for($i=1;$i<=4;$i++){
$r .= $s[rand(0,count($s)-1)];
}
$_SESSION['nb'] = $r;

?>

然后寫Ajax代碼如下：

function checkYZM(){
getXmlhttp();
xmlHttp.open("GET","chekYZM.php?YZM="+yzm.value,"false");
xmlHttp.onreadystatechange = function(){
if(xmlHttp.readyState ==4){
if(xmlHttp.status == 200){
var txt = parseInt(xmlHttp.responseText);
if(txt){
tS5.innerHTML = "驗證成功";
}else{
tS5.innerHTML = "驗證失敗";
}
}
}
}
xmlHttp.send(null);
}

?

最后在chekYZM.php頁面里進行判斷：

<?php
session_start();

if(isset($_GET['YZM'])){
$yzm = $_GET['YZM'];
if($yzm == $_SESSION['nb']){
echo"1";
}else{
echo"0";
}
}
?>

PHP中判斷輸入驗證碼是否一致