try below
if (FileUpload1.HasFile)
{
string FileName = Path.GetFileName(FileUpload1.PostedFile.FileName);
FileUpload1.SaveAs(Server.MapPath("~/" +Session["brandname"].ToString() +
"/" + Seasonfolders.SelectedItem.Text +"/" + stylefolders.SelectedItem.Text
"/" + Images +"/") + FileName );
Image1.ImageUrl = "/" +Session["brandname"].ToString() +
"/" + Seasonfolders.SelectedItem.Text +"/" + stylefolders.SelectedItem.Text
"/" + Images +"/" + FileName ;
}
Based on your comments, you are storing images outside the root folder. there are few ways to handle this situation.
check
Displaying images that are stored outside the Website Root Folder[
^]
Or Make D:\YourUploadFolder\ a virtual directory in the website using IIS management - then you could send URL to set the
Image1.ImageUrl