Use standard method of Form component (Brush method). This method has Bitmap method, which allows you to fill background of the form by images.
procedure TForm1.FormCreate(Sender: TObject); var MyBitmap: TBitmap; begin MyBitmap:=TBitmap.Create; MyBitmap.LoadFromFile('factory.bmp'); Form1.Brush.Bitmap:=MyBitmap; end;