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:=spnh.Value;
  if (X<=Image1.Width div 2) and (Y<=Image1.Height div 2) then Image1.Canvas.Pen.Color:=clRed;
  if (X>=Image1.Width div 2) and (Y>=Image1.Height div 2) then Image1.Canvas.Pen.Color:=clBlue;
  if (X>=Image1.Width div 2) and (Y<=Image1.Height div 2) then Image1.Canvas.Pen.Color:=clYellow;
  if (X<=Image1.Width div 2) and (Y>=Image1.Height div 2) then Image1.Canvas.Pen.Color:=clGreen;
  if Shift = [ssLeft] then Image1.Canvas.LineTo(X,Y);
end;