给图片添加文字水印

public void ImageWaterMarkText(string filename, ImageFormat format)
        {
            Image originalImage = Image.FromFile(filename);
            Graphics g = Graphics.FromImage(originalImage);

            Font drawFont = new Font("Arial", 12, FontStyle.Regular, GraphicsUnit.Pixel);　　　　　　　　　　 //找到图片旋转中点
            float xpos = originalImage.Width > originalImage.Height ? originalImage.Width -  originalImage.Height/ 2 : originalImage.Width / 2;
            float ypos = originalImage.Width > originalImage.Height ? originalImage.Height / 2 : originalImage.Height - originalImage.Width / 2;

            var triggleLeg = (originalImage.Width > originalImage.Height ? originalImage.Height : originalImage.Width) / 3;
            ar gPath = new GraphicsPath();
            gPath.AddLine(originalImage.Width - triggleLeg, originalImage.Height, originalImage.Width, originalImage.Height - triggleLeg);
            gPath.AddLine(originalImage.Width, originalImage.Height - triggleLeg, originalImage.Width, originalImage.Height);
            gPath.AddLine(originalImage.Width, originalImage.Height, originalImage.Width - triggleLeg, originalImage.Height);
            g.FillPath(new SolidBrush(Color.FromArgb(120, Color.Black)), gPath);
　　　　　　　　　　　　
            g.TranslateTransform(xpos, ypos);
            g.RotateTransform(-45);

            SizeF crSize;
            string watermarkText;                        watermarkText = "测试文字";
            crSize = g.MeasureString("Chine LianTong", drawFont);

            g.DrawString(watermarkText, drawFont, new SolidBrush(Color.Red), -crSize.Width / 2, 250);

            watermarkText = DateTime.Now.ToString("Current: yyyy-MM-dd HH:mm");
            g.DrawString(watermarkText, drawFont, new SolidBrush(Color.Red), -crSize.Width / 2, 250 + crSize.Height + 5);

            g.Dispose();

            MemoryStream stream = new MemoryStream();
            originalImage.Save(stream, format);
            originalImage.Dispose();

            Image img = Image.FromStream(stream);
            img.Save(filename);
            img.Dispose();

        }