php 验证码

var verifyURL="{:U('stage/verify','','')}";
 function change_code(obj){
        $("#code").attr("src",verifyURL+"/"+Math.random());
        return false;
}

<a href="javascript:void(change_code(this));">
<img src="{:U('stage/verify')}" id="code">看不清
</a>