Portraits in text like the statue of liberty are a great favourite of mine.
Nicholas Wade, Visual illusions, Lawrence Erlbaum 1990, prints many such portraits. Some of his portraits (in text and not in text) can be seen here. Some of the persons are really difficult to see. Looking at the screen from some yards away helps. The way the portraits are made in Wade's pictures is pure brilliance. One can appreciate them even more if one knows what these people are famous for.