php captcha图像脚本无法正常工作

I am having one captcha image on php. Can any body help in getting the refresh/ reload code. My php form code is given below.

<form action=" " method="post" name=" ">
CAPTCHA: <input type="text" name="name" />
<img src=" " id="captcha" />
<input type="submit" value="SUBMIT" name="submit" />
</form>

Your question is not specific. As per my understanding, you require reload captcah iamge with out refreshing the entire page, then you may use javascript.

<script type="text/javascript">
function reloadImg() {
    var d=new Date();
    document.getElementById("captcha").src="http://www.yourfile.php?a="+d.getTime();
}

Check here the demo: