以下代码本人调试全部通过。运行authpage.php。 

<? 

/* 

* Filename: authpage.php 

*/ 

srand((double)microtime()*1000000); 

//验证用户输入是否和验证码一致 

if(isset($_POST['authinput'])) 

{ 


if(strcmp($_POST['authnum'],$_POST['authinput'])==0) 

echo "验证成功！"; 

else 

echo "验证失败！"; 

} 

//生成新的四位整数验证码 

while(($authnum=rand()%10000)<1000); 

?> 

<form action=authpage.php method=post> 

<table> 

请输入验证码：<input type=text name=authinput style="width: 80px"><br> 

<input type=submit name="验证" value="提交验证码"> 

<input type=hidden name=authnum value=<? echo $authnum; ?>> 

<img src=authimg.php?authnum=<? echo $authnum; ?>> 

</table> 

</form> 

------------------------------------------------------------------------------------------------------------- 

<? 
/* 

* Filename: authimg.php 

*/ 
//生成验证码图片 
Header("Content-type: image/PNG"); 

srand((double)microtime()*1000000); 

$im = imagecreate(58,28); 

$black = ImageColorAllocate($im, 0,0,0); 

$white = ImageColorAllocate($im, 255,255,255); 

$gray = ImageColorAllocate($im, 200,200,200); 

imagefill($im,68,30,$gray); 

//将四位整数验证码绘入图片 

imagestring($im, 5, 10, 8, $HTTP_GET_VARS['authnum'], $white); 

for($i=0;$i<50;$i++) //加入干扰象素 

{