image delete from folder in edit opreation

in edit opreation when click update image then delete old image from folder like database....

protected void Page_Load(object sender, EventArgs e)

{

if (!IsPostBack)

{

string id = Request.QueryString["id"].ToString();

string photo = Request.QueryString["image1"].ToString();

editdata(id);

LoadImage(id);

imgdltdata(id,photo);

}

private void imgdltdata(string id, string photo)

{

string qry = "delete from appformtbl where photo=" + photo + " id=" + id + "";

System.IO.File.Delete(image1.PostedFile.FileName);

}

this is my code.....

i got error Object reference not set to an instance of an object.

in string photo.....

plz someone help me......