사용방법

WindowSnap(Self.Handle, Image1.Picture.Bitmap) ;
Image1.Refresh;

함수선언

function WindowSnap(windowHandle: HWND; bmp: TBitmap): boolean;
var
  r: TRect;
  user32DLLHandle: THandle;
  printWindowAPI: function(sourceHandle: HWND; destinationHandle: HDC; nFlags: UINT): BOOL; stdcall;
begin
  result := False;
  user32DLLHandle := GetModuleHandle(user32) ;
  if user32DLLHandle <> 0 then
  begin
    @printWindowAPI := GetProcAddress(huser32, 'PrintWindow') ;
    if @printWindowAPI <> nil then
    begin
      GetWindowRect(windowHandle, r) ;
      bmp.Width := r.Right - r.Left;
      bmp.Height := r.Bottom - r.Top;
      bmp.Canvas.Lock;
      try
        result := printWindowAPI(windowHandle, bmp.Canvas.Handle, 0) ;
      finally
        bmp.Canvas.Unlock;
      end;
    end;
  end;
end; (*WindowSnap*)

출처 : http://delphi.about.com/od/delphitips2008/qt/print_window.htm