public ActionResult Index()
        {
            byte[] fileBytes = System.IO.File.ReadAllBytes(Path.Combine(HttpContext.Server.MapPath("~/content/Site.css")));
            return File(fileBytes, System.Net.Mime.MediaTypeNames.Application.Octet, "Site.css");
        }

  public String ImgToBase64String(string fileName)
        {
            FileInfo file = new FileInfo(fileName);
            var stream = file.OpenRead();
            byte[] buffer = new byte[file.Length];
            //读取图片字节流
            stream.Read(buffer, 0, Convert.ToInt32(file.Length));
            //将字节流转化成base64字符串
           return Convert.ToBase64String(buffer);
        }

 item.DocBase64SR = "data:image/png;base64," + new InspectionRatingSeeModel().ImgToBase64String(Uri);