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");