ASCII код для PrintScreen

Вариант 1:

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics,
  Controls, Forms, Dialogs;

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
    procedure AppIdle(Sender: TObject; var Done: Boolean);
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.AppIdle(Sender: TObject; var Done: Boolean);
begin
if GetAsyncKeyState(VK_SNAPSHOT) <> 0 then
  Form1.Caption := 'PrintScreen ia?aoa !';
  Done := True;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Application.OnIdle := AppIdle;
end;

end.

Вариант 2:

Source: https://forum.sources.ru

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
    procedure WMHotKey(var Msg : TWMHotKey); message WM_HOTKEY;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

const id_SnapShot = 101;

procedure TForm1.WMHotKey (var Msg : TWMHotKey);
begin
  if Msg.HotKey = id_SnapShot then
    ShowMessage('GotIt');
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  RegisterHotKey(Form1.Handle,
                 id_SnapShot,
                 0,
                 VK_SNAPSHOT);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  UnRegisterHotKey (Form1.Handle, id_SnapShot);
end;