idHTTP.Post('http://vk.com/upload.php', Params, Content);

procedure TMainForm.IdHTTP1Work(ASender: TObject; AWorkMode: TWorkMode;
  AWorkCount: Integer);
beign
  If AWorkMode = wmWrite Then { Действия }
end;

procedure TMainForm.IdHTTP1Work(ASender: TObject; AWorkMode: TWorkMode;
  AWorkCount: Integer);
beign
  If AWorkMode = wmWrite Then { Действия }
end;

var k:Integer;
procedure HTTPWork(Sender: TObject; AWorkMode: TWorkMode;
  const AWorkCount: Integer);
begin
  if k<>0 then
    Progress.Position := Round(AWorkCount / k * 100) // подсчет процентов %
end;
procedure HTTPWorkBegin(Sender: TObject; AWorkMode: TWorkMode;
  const AWorkCountMax: Integer);
begin
  if AWorkMode=wmWrite then
    k:= AWorkCountMax;  // запомнить размер отправляемого
end;