Primeiro adicione no seu form os componentes TButton, TImage e TEdit.

unit Unit1;
  interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls, ExtCtrls;
type
  TForm1 = class(TForm)
  Image1: TImage;
  Button1: TButton;
  Edit1: TEdit;
  procedure Button1Click(Sender: TObject);
  procedure FormShow(Sender: TObject);
private
  { Private declarations }
public
 { Public declarations }
  function GeraImagem(Img: TImage): string;
end;
 

var
  Form1: TForm1;
  validapost : string;
implementation
{$R *.dfm}
{ TForm1 }
function TForm1.GeraImagem(Img: TImage): string;
  const
    f: array [0..4] of string =  ('Courier New', 'Impact', 'Times New Roman', 'Verdana', 'Arial');
    s = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
    C : ARRAY [0..14] OF tcOLOR = (clAqua, clBlack, clBlue, clFuchsia, clGray, clGreen, clLime, clMaroon, clNavy, clOlive, clPurple, clRed, clSilver, clTeal, clYellow);
 

var
  i, x, y : integer;
  r : string;
begin
  randomize;
  Img.Width := 160;
  Img.Height := 60;
  for i := 0 to 3 do
  r := r + s[Random(length(s)-1)+1];
  with Img.Picture.Bitmap do
  begin
    width := Img.Width;
    Height := Img.Height;
    Canvas.Brush.Color := $00EFEFEF;
    Canvas.FillRect(Img.ClientRect);
    for i := 0 to 3 do
    begin
      Canvas.Font.Size := random(20) + 20;
      Canvas.Font.Name := f[High(f)];
      Canvas.Font.Color := c[random(High(c))];
      Canvas.TextOut(i*40,0,r[i+1]);
    end;
    for i := 0 to 2 do
    begin
      Canvas.Pen.Color := c[random(High(c))];
      Canvas.Pen.Width := 2;
      canvas.MoveTo(random(Width),0);
      Canvas.LineTo(random(Width),Height);
      Canvas.Pen.Width := 1;
      x := random(Width-10);
      y := random(Height-10);
      Canvas.Rectangle(x,y,x+10,y+10);
    end;
  end;
  Result := r;
end;
 

procedure TForm1.Button1Click(Sender: TObject);
begin
  if (Edit1.Text = validapost) then
    Application.MessageBox('Parabéns, muito bem','Sucesso',
  MB_OK + MB_ICONINFORMATION);
  FormShow(self);
end;
 

procedure TForm1.FormShow(Sender: TObject);
begin
  validapost := GeraImagem(Image1);
end;
 

end.