procedure TForm1.FormCreate(Sender: TObject);
 var
   Bmp: TBitmap;
 begin
   Bmp := TBitmap.Create;
   try
    Bmp.LoadFromFile('C:\2.bmp');
     SetWindowRGN(Form1.Handle, BitmapToRegion(bmp,clwhite), True);
   finally
     Bmp.Free;
   end;
end;