How to make Captcha in unigui?

unit UniCaptcha;

interface
uses
  classes,
  Graphics,
  uniImage;

type TUniCaptcha=class(TUniImage)
  private
    FChallenge:ShortString;
    procedure Render;
  public
    constructor create(Owner:TComponent);override;
    procedure SetChallenge(aChallenge :ShortString);
  published
    property Challenge  :ShortString    read FChallenge   write FChallenge;
end;

procedure Register;

implementation

constructor TUniCaptcha.Create(Owner:TComponent);
begin
  inherited;
end;

procedure TUniCaptcha.SetChallenge(aChallenge:ShortString);
begin
  FChallenge:= aChallenge;
  Render;
end;

procedure TUniCaptcha.render;
Var
  b :TBitmap;
  i :Integer;
begin
  b :=TBitmap.Create;
  with b do
  begin
    b.Width  :=self.Width;
    b.height :=self.Height;
    For i :=0 to 30dobegin
      randomize;
      canvas.Pen.Width     := random(5)+5;
      Canvas.Pen.Color     := random(64738)+64738;
      Canvas.Brush.Style   := bsFDiagonal;

      Canvas.Ellipse(random(width),random(Height),random(width),random(height));
    end;
    Canvas.Font.Color:= clBlue;
    Canvas.Font.Size  :=18;
    Canvas.TextOut(10,trunc(self.height/2),FChallenge);
    Canvas.Font.Color:= clRed;
    Canvas.TextOut(8,trunc(self.height/2)-2,FChallenge);
  end;

  Picture.Assign(B);
  b.Free;
end;

procedure Register;
begin
    RegisterComponents('UniCustom',[TUniCaptcha]);
end;

end.