动态生成image的问题，急，请大家帮忙！

下面这个过程，为什么呢最后在imgdrawingpad.canvas上显示不了我画出来的图形呢？
procedure TForm1.CreateImg;
var Im:TIMage;
begin
Screen.cursor:=crDefault;
    im:=TImage.Create(self) ;
    im.Parent:=sbxMain;
    im.Stretch:=true;
    im.Left:=200;
    im.Top:=200;
    im.Transparent:=true;
    im.Visible:=true;
    im.height:=30;
    im.width:=20;
    im.Canvas.Pen.Mode:=pmCopy;
    im.Canvas.Pen.Color:=clred;
    im.Canvas.MoveTo(100,100);
    im.Canvas.LineTo(110,100);
    im.Canvas.Rectangle(100,90,120,110);
    im.Canvas.MoveTo(120,100);
    im.Canvas.LineTo(130,100);
    imgdrawingpad.Canvas.CopyRect(rect(100,90,130,110),im.Canvas,rect(100,90,130,110));
    im.OnMouseDown:=form1.ImgMouseDown;
    im.OnMouseMove:=form1.ImgMouseMove;
    im.OnMouseUp:=form1.ImgMouseUp;
       end;