Asp.net(C#)给图片加上水印效果

下面的代码中，加文字水印和加图片水印的代码不能共存，这里是为了方便显示才写在一块的
 

private void Btn_Upload_Click(object sender, System.EventArgs e)
{
 if(UploadFile.PostedFile.FileName.Trim()!="")
 {
 //上传文件
string extension = Path.GetExtension(UploadFile.PostedFile.FileName).ToUpper();
 string fileName = DateTime.Now.Year.ToString() + DateTime.Now.Month.ToString() + DateTime.Now.Day.ToString() + DateTime.Now.Hour.ToString() + DateTime.Now.Minute.ToString() + DateTime.Now.Second.ToString();
 string path = Server.MapPath(".") + "/UploadFile/" + fileName + extension;
 UploadFile.PostedFile.SaveAs(path);

 //加文字水印，注意，这里的代码和以下加图片水印的代码不能共存
System.Drawing.Image image = System.Drawing.Image.FromFile(path);
 Graphics g = Graphics.FromImage(image);
 g.DrawImage(image, 0, 0, image.Width, image.Height);
 Font f = new Font("Verdana", 32);
 Brush b = new SolidBrush(Color.White);
 string addText = AddText.Value.Trim();
 g.DrawString(addText, f, b, 10, 10);
 g.Dispose();

 //加图片水印
System.Drawing.Image image