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，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.ToString("yyyyMMddhhmmss");
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 = System.Drawing.Image.FromFile(path);
System.Drawing.Image copyImage = System.Drawing.Image.FromFile( Server.MapPath(".") + "/Alex.gif");
Graphics g = Graphics.FromImage(image);
g.DrawImage(copyImage, new Rectangle(image.Width-copyImage.Width, image.Height-copyImage.Height, copyImage.Width, copyImage.Height), 0, 0, copyImage.Width, copyImage.Height, GraphicsUnit.Pixel);
g.Dispose();
//保存加水印过后的图片,删除原始图片
string newPath = Server.MapPath(".") + "/UploadFile/" + fileName + "_new" + extension;
image.Save(newPath);
image.Dispose();
if(File.Exists(path))
{
File.Delete(path);
}
Response.Redirect(newPath);
}
}