put byte[] of PostedFile to the session and access it next time
Stream fs = fileUpl.PostedFile.InputStream;
BinaryReader br = new BinaryReader(fs);
Session["bytes"] = br.ReadBytes((Int32)fs.Length);
then
byte[] bytes = (byte[])Session["bytes"]
string base64String = Convert.ToBase64String(bytes, 0, bytes.Length);
Image1.ImageUrl = "data:image/png;base64," + base64String;