dynamically create an image control with fileupload

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ASP.NET

I have a fileupload and a button control button on my webform(asp.net 2010).

What i want is , as soon as i click on the button to upload the file(image), it should dynamically create an image control and set the imageurl to be the one which i just uploaded. And the image should be displayed...however , it is not working..please help me giving a reason..Following si the code :-

protected void Button1_Click(object sender, EventArgs e)
    {
string str=FileUpload1.FileName;
    string path=Server.MapPath("image");
        string fulpath=path + "\\" + str;
        FileUpload1.PostedFile.SaveAs(fulpath);
        Image img = new Image();
        Page.Form.Controls.Add(img);
        img.ImageUrl = Server.MapPath(str);
    }