织梦ajax跨域提交自定义表单和跨域验证码问题

A站(www.a.com)，有个form表单，ajax提交到 B站(www.b.com)，还附带个验证码

A站上的表单代码如下

<script type="text/javascript" src="http://apps.bdimg.com/libs/jquery/1.6.4/jquery.min.js"></script>

<script>
function send(){
    $.ajax({
        cache:true,type:"POST",url:"http://www.b.com/plus/diy.php",data:$('#diyform').serialize(),xhrFields:{withCredentials: true},//ajax跨域提交需要
		crossDomain:true,//ajax跨域提交需要
        success: function(data){
            if(data=="success"){
                alert('发送成功!');
            }else{
                alert('发送失败!');
            }
        }
    });
}
</script>

	<form action="" enctype="multipart/form-data" method="post" id="diyform">
		<input type="hidden" name="action" value="post" /> <input type="hidden" name="diyid" value="2" /> <input type="hidden" name="do" value="2" /> <input type="hidden" name="dede_fields" value="name,text" /> <input type="hidden" name="dede_fieldshash" value="c2be5bb5ec45d9d01ca9f60dc469b3fb" /> 
		<p>
			姓名： <input type="text" name="name" id="name" /> 
		</p>

		<p>
			验证码： <input type="text" name="validate" /><img src="http://www.b.com/include/vdimgck.php" align="absmiddle" onclick="this.src='http://www.b.com/include/vdimgck.php?tag='+Math.random();" style="cursor:pointer;" /> 
		</p>

		<div onclick="send()">
			提交
		</div>

	</form>

1、提交到 http://www.b.com/plus/diy.php

2、验证码 http://www.b.com/include/vdimgck.php

3、ajax 跨域必需js代码

xhrFields:{withCredentials: true},crossDomain:true,

B站上的 /plus/diy.php 文件上面加入

header("Access-Control-Allow-Credentials:true"); 
header("Access-Control-Allow-Origin:http://www.a.com");