Madame Tussaud's Wax Museum has been around for centuries - since the French Revolution. But when it began it was the only place to see famous people. But a century of news magazines and papers, television and now the Internet where celebrity news is always accompanied by photos or video means the museum has long outlived its original function. This year, Madame Tussaud's is set to open two new museums. So what's the secret of its success in a digital world? Can it only get stronger as we become more obsessed with celebrity?