// http://aggpasmod.sourceforge.net/

uses
  AggColor, Agg2D, Agg2DGraphics;

procedure TForm1.Button1Click(Sender: TObject);
var
  Bitmap: TBitmap;
  AggColor: TAggRgba8;
  AggEngine: TAgg2DGraphics;
begin
  AggEngine := TAgg2DGraphics.Create;
  try
    Bitmap := TBitmap.Create;
    try
      Bitmap.LoadFromFile('C:\SomeFile.bmp');

      AggEngine.Attach(Bitmap);
      AggEngine.NoLine;
      AggColor.Initialize(255, 255, 255, 25);
      AggEngine.FillColor := AggColor;
      AggEngine.FlipText := True;
      AggEngine.Font('Arial', 52, True, False, fcVector);
      AggEngine.Text(16, 80, 'Watermark!');

      Canvas.Draw(0, 0, Bitmap);
    finally
      Bitmap.Free;
    end;
  finally
    AggEngine.Free;
  end;
end;