Written by Scott Smith GREENWICH, CT — Once upon a time, visual artists had to forge their way toward success using such primitive forms of marketing as opening their studios, cultivating buyers, charming the pants off of gallerists, and creatively spreading word of mouth. Today there's Instagram, a platform where artists can show off the gift that produces their work, but, even more than that, can inspire literally tens of thousands or even hundreds of thousands of people to follow them and to engage in a rich, spirited, ongoing dialogue about their work. The Artists of Instagram...