网络图片转base64

   public static Image UrlToImage(string url)
        {
            try
            {
                WebClient mywebclient = new WebClient();
                byte[] Bytes = mywebclient.DownloadData(url);
                using (MemoryStream ms = new MemoryStream(Bytes))
                {
                    Image outputImg = Image.FromStream(ms);
                    return outputImg;
                }
            }
            catch (Exception ex)
            {
                return null;
            }
        }

        public static string ImageToBase64(Image img)
        {
            try
            {
                Bitmap bmp = new Bitmap(img);
                MemoryStream ms = new MemoryStream();
                bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
                byte[] arr = new byte[ms.Length];
                ms.Position = 0;
                ms.Read(arr, 0, (int)ms.Length);
                ms.Close();
                return Convert.ToBase64String(arr);
            }
            catch (Exception ex)
            {
                return null;
            }
        }

引用

   string base64 = PicUrlToBase64.ImageToBase64(PicUrlToBase64.UrlToImage(url));

注意 版本问题 版本太高 会报错