Exemplo using

                using (Graphics graphics = Graphics.FromImage(resized))
                {
                    graphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                    graphics.SmoothingMode = SmoothingMode.HighQuality;
                    graphics.CompositingQuality = CompositingQuality.HighQuality;
                    graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;

                    graphics.DrawImage(imagemOriginal, new Rectangle(0, 0, resized.Width, resized.Height), new Rectangle(0, 0, imagemOriginal.Width, imagemOriginal.Height), GraphicsUnit.Pixel);

                    if (addWaterMark == "1")
                    {
                        string filePath = context.HttpContext.Server.MapPath("~/Content/logotrans.png");

                        if (File.Exists(filePath))
                        {
                            using (Bitmap bmLogo = new Bitmap(filePath))
                            {

                                int widthLogo = bmLogo.Width;
                                int heightLogo = bmLogo.Height;

                                const int posHorizontal = 20;
                                const int posVertical = 20;

                                graphics.DrawImage(bmLogo, new Point(posHorizontal, posVertical));
                            }
                        }
                    }                    
                }

                const int quality = 90;
                System.Drawing.Imaging.EncoderParameters encoderParameters = new System.Drawing.Imaging.EncoderParameters(1);
                encoderParameters.Param[0] = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)quality);

                byte[] buffer = null;

                using (MemoryStream stream = new MemoryStream())
                {
                    resized.Save(stream, GetImageCodeInfo("image/jpeg"), encoderParameters);
                    buffer = stream.ToArray();
                }