Now in its 245th year, and with 12,000 submissions, the Royal Academy's Summer Exhibition is the largest open art exhibition in the world. In this Culture Show special, art critic Alastair Sooke asks what makes someone an artist and why do they do it? He hears from curators, art dealers, and of course the artists themselves. From Sunday painters to international contemporary artists, from traditional landscapes to giant sculptures made from bottle tops, the Summer Exhibition is the British art scene laid bare.