procedure TForm1.Image1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  Image1.Canvas.MoveTo(X,Y);
end;

procedure TForm1.Image1MouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  Image1.Canvas.Pen.Width:=5;
  Image1.Canvas.Pen.Color:=clBlue;
  if Shift = [ssLeft] then Image1.Canvas.LineTo(X,Y);
  if Shift = [ssRight] then
    begin
      Image1.Canvas.Pen.Color:=clWhite;
      Image1.Canvas.Ellipse(X-5,Y-5,X+5,Y+5);
    end;
  Image1.Canvas.Pen.Width:=1;
  Image1.Canvas.Pen.Color:=clBlack;
end;