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();
}