public static string ImgToBase64String(Bitmap bmp)        {            try            {                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;            }        }

只需要传入一个Bitmap对象，亲测可用哈。返回给前台时，将转换成base64的码前面加上

data:image/png;base64,

例如：

Bitmap bt;            string base64Img = ImgToBase64String(bt);            this.Image1.ImageUrl = "data:image/png;base64," + base64Img;