Amazon launched an online bookstore two decades ago. Since then, the Internet has been changing the way readers buy books. Paris has been a major book-selling city since the 17th century, when the first bouquinistes began lining the banks of the Seine. The 240 bouquinistes sell everything from the rare to the out-of-print, but now they face a serious threat from Internet sellers. BBC takes a look at these unique Parisian booksellers on the precipice of either evolution or extinction.