This article explains how to make an watermark in an image, in runtime, with asp.net.
First create an aspx page, here it is default.aspx.This page is for uploading image.
















We have selected the image,text,color and file name in which we want to save the image.

Now we are going to pass these values to another page which is the watermark generator page.

protected void Button1_Click(object sender, EventArgs e)
    {
        FileUpload1.PostedFile.SaveAs(Server.MapPath(FileUpload1.FileName));
        string path = FileUpload1.FileName;
        Response.Redirect("watermarktest.aspx?text="+TextBox1.Text+"&;image="+path+"&saveas="+TextBox2.Text+"&color="+DropDownList1.SelectedItem.Text);
    }


here it is watermarktest.aspx. Now we are going to use this values to create watermark.
protected void Page_Load(object sender, EventArgs e)
{
string fn = Request.QueryString["saveas"]+".jpg";
string filename = Request.MapPath(Request.QueryString["image"]);
string text = Request.QueryString["text"];
string textcolor = Request.QueryString["color"];

Bitmap objBMP = (Bitmap)Bitmap.FromFile(filename);

Graphics objGraphics = System.Drawing.Graphics.FromImage(objBMP);

int h, w;
h = objBMP.Height - 50;
w =10;
objGraphics.TextRenderingHint = TextRenderingHint.ClearTypeGridFit;
//' Configure font to use for text
Font objFont = new Font("Arial", 20,GraphicsUnit.Pixel);
Color color = new Color();
if (textcolor == "Black")
{

color = Color.FromArgb(70, 0, 0, 0);
}
else if (textcolor == "White")
{

color = Color.FromArgb(70, 255, 255, 255);
}
SolidBrush brush = new SolidBrush(color);


//' Write out the text
objGraphics.DrawString(text,objFont,brush,w,h);


//' Set the content type and return the image
Response.ContentType = "image/JPEG";

objBMP.Save(Response.OutputStream, ImageFormat.Jpeg); // Displays the image
objBMP.Save(Server.MapPath(fn), ImageFormat.Jpeg); //Replaces the selected image with the watermarked image

objFont.Dispose();
objGraphics.Dispose();

objBMP.Dispose();
File.Delete(Server.MapPath(Request.QueryString["image"]));
}



And the result is