Michael H. Miller has a spectacular post on Gallerist NY chronicling the burgeoning use of Instagram as a selling medium for second-market works:

Even if most gallery owners aren’t selling works directly through Instagram, people are starting to make attempts, and iPhone dealing is a new reality to grapple with. […]

For dealers, it’s quite possibly the easiest way of selling art—several sources mentioned stirring up interest from collectors accidentally through casually posting images of their back rooms. ([Gavin]Brown, who prefers to just let the random stream of images “all come at you,” does not use Instagram this way, though he did try to sell a Jeremy Deller print on Tumblr. “It didn’t work,” he said.) Art advisers are scheduling studio visits with undiscovered artists through their Instagram accounts. Collectors, too, create de facto advertisements for themselves by showing people what they have. Alberto Mugrabi recently posted a painting that he owns from Warhol’s Marilyn Monroe series

The Gallery Unfiltered: On the Art World’s Obsession with Instagram (Gallerist NY)