/// <summary>
        /// 圖片加水印文字
        /// </summary>
        /// <param name="imgPath">原圖片路徑</param>
        /// <param name="newImgPath">新圖片路徑</param>
        /// <param name="text">水印文字</param>
        /// <param name="Alpha">透明度</param>
        ///
 
 <param name="fontsize">字體大小</param>
        public static bool PicAddWaterText(string imgPath,string newImgPath, string text, int Alpha = 1, int fontsize = 30)
        {
            try
            {
                //text = text + "僅限xx使用";
                //System.Drawing.Image imgPhoto = System.Drawing.Image.FromStream(oldstream);
 
//文件流
                System.Drawing.Image imgPhoto = System.Drawing.Image.FromFile(imgPath);
                int imgPhotoWidth = imgPhoto.Width;
                int imgPhotoHeight = imgPhoto.Height;

                Bitmap bmPhoto = new Bitmap(imgPhotoWidth, imgPhotoHeight, System.Drawing.Imaging.PixelFormat.Format24bppRgb);

                bmPhoto.SetResolution(
 
72, 72);
                Graphics gbmPhoto = Graphics.FromImage(bmPhoto);
                //gif背景色
                gbmPhoto.Clear(Color.FromName("White"));
                gbmPhoto.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
                gbmPhoto.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                gbmPhoto.DrawImage(imgPhoto, new Rectangle(0, 0, imgPhotoWidth, imgPhotoHeight), 0, 0, imgPhotoWidth, imgPhotoHeight, GraphicsUnit.Pixel);
                imgPhoto.Dispose();
                System.Drawing.Font font = null;
                System.Drawing.SizeF crSize = new SizeF();
                font = new Font("宋體", fontsize, FontStyle.Regular);
                //測量指定區域
                crSize = gbmPhoto.MeasureString(text, font);
                float y = (imgPhotoHeight - crSize.Height)/2;
                float x = (imgPhotoWidth - crSize.Width)/2;
                System.Drawing.StringFormat StrFormat = new System.Drawing.StringFormat();
                StrFormat.Alignment = System.Drawing.StringAlignment.Center;                
                //畫兩次制造透明效果
                var writeColor = Color.FromArgb(Alpha, System.Drawing.ColorTranslator.FromHtml("#999"));
                //var writeColor = Color.FromArgb(255, Color.Red);
                //System.Drawing.SolidBrush semiTransBrush2 = new System.Drawing.SolidBrush(Color.FromArgb(Alpha, Color.Red));
                System.Drawing.SolidBrush semiTransBrush2 = new System.Drawing.SolidBrush(writeColor);
               
                //float _x = -20, _y = y + 10;
                //if (imgPhotoHeight > imgPhotoWidth)
                //{
                //   // gbmPhoto.RotateTransform(-60);
                //    _y = 0; _x = 0;
                //}
                //else { gbmPhoto.RotateTransform(320); }
                gbmPhoto.TranslateTransform(x,y);
                var Var_trans = gbmPhoto.Transform;
                Var_trans.Shear(0.4F,0.00F);
                gbmPhoto.Transform = Var_trans;
                //gbmPhoto.DrawString(text, font, semiTransBrush2, _x, _y);
                // gbmPhoto.DrawString(text, font, semiTransBrush2, imgPhotoWidth, imgPhotoHeight / 2);
                gbmPhoto.DrawString(text, font, semiTransBrush2, 10, 10);
                //gbmPhoto.DrawString(text, font, semiTransBrush2, 0, y);


                //System.Drawing.SolidBrush semiTransBrush = new System.Drawing.SolidBrush(writeColor);
                // gbmPhoto.DrawString(text, font, semiTransBrush, _x, _y);
                //gbmPhoto.DrawString(text, font, semiTransBrush, imgPhotoWidth / 2, imgPhotoHeight / 2);
                //gbmPhoto.DrawString(text, font, semiTransBrush, 0, y);

                //gbmPhoto.DrawString(text, font, semiTransBrush2, 0, y);
                //Stream newStream = new MemoryStream();

                bmPhoto.Save(newImgPath, System.Drawing.Imaging.ImageFormat.Jpeg);

                gbmPhoto.Dispose();               
                bmPhoto.Dispose();
                //imgPhoto1.Dispose();
                return true;
            }
            catch (Exception e)
            {
                return false;
            }
        }

分享一段，圖片加水印的代碼。本人修改過多次