启用 CORS 来解决这个问题（ajax跨域请求）

 <input type="file" name="btn_Upload" value="上传" id="btn_Upload" />
 <img src="" alt="" id="img_Upload" />

 @section Scripts
 {
     <link href="../../js/uploadifive-v1.2.2-standard/uploadifive.css" rel="stylesheet" />
     <script src="../../js/uploadifive-v1.2.2-standard/jquery.uploadifive.js"></script>
 }

 <script>
     $(function () {
         $('#btn_Upload').uploadifive({
             formData: { openId: '@ViewBag.OpenId' },
             multi: false,
             uploadScript: '@WXCommon.ConfigHelper.UploadUrl',
             onUploadComplete: function (file, data) {
                 if (data) {
                     var json = $.parseJSON(data);
                     if (json.res) {
                         alert(json.msg);
                         $('#img_Upload').attr({
                             src: '@WXCommon.ConfigHelper.ThumbnailPath' + '/' + '@ViewBag.OpenId' + '/' + json.fileName
                         });
                     } else {
                         alert(json.msg);
                     }
                 } else {
                     alert('服务器内部错误!');
                 }
             }
         });
     });
 </script>

Javascript

 //独立部署的图片服务器
 public ActionResult Index()
 {
     //if (Request.HttpMethod == "OPTION")
     //{
     //    Response.AddHeader("Access-Control-Allow-Methods", "GET,POST");
     //    Response.AddHeader("Access-Control-Allow-Headers", "Content-Type,Accept");
     //    Response.AddHeader("Access-Control-Max-Age", "1728000");
     //    Response.AddHeader("Access-Control-Allow-Origin", "*");
     //}
     string openId = Request["openId"];
     HttpPostedFileBase httpPostedFileBase = Request.Files["Filedata"];
     string fileName = httpPostedFileBase.FileName;
     string extensionName = System.IO.Path.GetExtension(fileName).ToLower();
     if (extensionName == ".jpg" || extensionName == ".jpeg")
     {
         string virtualPath = "/uploads" + "/" + fileName.Replace(extensionName, "") + DateTime.Now.ToString("yyyyMMddhhmmss") + extensionName;
         string fullPath = Server.MapPath(virtualPath);
         httpPostedFileBase.SaveAs(fullPath);

         string savePath = Server.MapPath("/thumbnails" + "/" + openId);
         string thumbnailFileName = Thumbnail.GetThumbnailImage(, , fullPath, savePath, System.Drawing.Imaging.ImageFormat.Jpeg);
         //删除原始文件
         //System.IO.File.Delete(fullPath);
         NowModel model = new NowModel();
         model.Id = ;
         model.OpenId = openId;
         model.FileName = thumbnailFileName;
         nowBLL.Insert(model);
         return Json(new { res = true, msg = "上传成功!", fileName = thumbnailFileName });
     }
     return Json(new { res = false, msg = "上传失败!" });
 }

ASP.Net

   <!--仅试用于IIS7以上版本，IIS6.0请用Response.AddHeader的方式-->
   <system.webServer>
     <validation validateIntegratedModeConfiguration="false" />
     <httpProtocol>
       <customHeaders>
         <add name="Access-Control-Allow-Origin" value="*"/>
         <add name="Access-Control-Allow-Methods" value="GET,POST,OPTION"/>
         <add name="Access-Control-Allow-Headers" value="Content-Type,soapaction"/>
       </customHeaders>
     </httpProtocol>
   </system.webServer>

图片服务器配置文件