C# 图片转换为base64

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WebRequest webRequest = WebRequest.Create("验证码url");            WebResponse webResponse = webRequest.GetResponse();            Stream stream = webResponse.GetResponseStream();            string cookie = webResponse.Headers.Get("Set-Cookie");            Image img = Bitmap.FromStream(stream);            pictureBox1.Image = img;            using (MemoryStream ms1 = new MemoryStream())            {                img.Save(ms1, System.Drawing.Imaging.ImageFormat.Jpeg);                byte[] arr1 = new byte[ms1.Length];                ms1.Position = 0;                ms1.Read(arr1, 0, (int)ms1.Length);                ms1.Close();                textBox1.Text = Convert.ToBase64String(arr1);            }

　　因为要做验证码识别第三方接口对接 需要将图片转换为base64传递参数 记录一下