The best-selling artist of all time?

If you tried to guess who was the best-selling artist of all time, the first names that would come to mind might be van Gogh or Picasso. But a moment's reflection tells us that the world doesn't work like that. A more considered answer might be Charles Schulz or Matt Groening - Messrs Peanuts and Simpsons respectively. The truth could hardly be more different or more surprising, at least according to the publisher HarperCollins, which says the world's bestseller is a Swiss religious artist by the name of Annie Vallotton.