dedecms自定义表单增加验证码的方法分享

<input name="validate" type="text" id="vdcode" style="text-transform:uppercase;" size="8"/> 
<img id="vdimgck" align="absmiddle" onClick="this.src=this.src+'?'" style="cursor: pointer;" alt="看不清？点击更换" src="../include/vdimgck.php"/> 
<a href="javascript:vide(-1);" onClick="changeAuthCode();">看不清？ </a> 

<script type="text/javascript" language="javascript"> 
//验证码 
function changeAuthCode() { 
var num = new Date().getTime(); 
var rand = Math.round(Math.random() * 10000); 
num = num + rand; 
$('#ver_code').css('visibility','visible'); 
if ($("#vdimgck")[0]) { 
$("#vdimgck")[0].src = "../include/vdimgck.php?tag=" + num;//这里写的域名地址如http://www.zhishiwu.com 
} 
return false; 
} 
</script> 

if(!empty($dede_fields)) 
{ 
$validate = empty($validate) ? '' : strtolower(trim($validate)); $svali = strtolower(GetCkVdValue()); 
if(($validate=='' || $validate != $svali) && preg_match("/6/",$safe_gdopen)){ ResetVdValue(); 
ShowMsg('验证码不正确!',$dede_add,0,1000); 
exit; 
}