[NumLock]

procedure TCanvas.StretchDraw(const Rect: TRect; Graphic: TGraphic);

пример:

Код:

type
  TForm1 = class(TForm)
    Image1: TImage;
    procedure FormPaint(Sender: TObject);
...
procedure TForm1.FormPaint(Sender: TObject);
begin
  Canvas.StretchDraw(Rect(0, 0, ClientWidth, ClientHeight), Image1.Picture.Graphic);
end;