class FormatChange
  {
    public static string ChangeImageToString(Image image)
    {
      try
      {
        MemoryStream ms = new MemoryStream();
        image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
        byte[] arr = new byte[ms.Length];
        ms.Position = 0;
        ms.Read(arr, 0, (int)ms.Length);
        ms.Close();
        string pic = Convert.ToBase64String(arr);

        return pic;
      }
      catch (Exception)
      {
        return "Fail to change bitmap to string!";
      }
    }

    public static Image ChangeStringToImage(string pic)
    {
      try
      {
        byte[] imageBytes = Convert.FromBase64String(pic);
        //读入MemoryStream对象
        MemoryStream memoryStream = new MemoryStream(imageBytes, 0, imageBytes.Length);
        memoryStream.Write(imageBytes, 0, imageBytes.Length);
        //转成图片
        Image image = Image.FromStream(memoryStream);

        return image;
      }
      catch (Exception)
      {
        Image image = null;
        return image;
      }
    }
  }