NEW YORK ( TheStreet) -- Simon Moss has discovered that Web media giants such as Facebook ( FB), Twitter and LinkedIn ( LNKD) face a shadowy competitor. "Dark social is what is driving my business now," Moss told me over the phone. The recently transplanted Australian is deep in the business of staying in touch with what works with the Web in these grim digital days. He's raised $2.2 million on the most interesting media start-up idea I've seen in months. Called ImageBrief, this eight-person New York-based digital photography market matches the unpublished images of top-flight professional photographers with first-rate media companies and advertisers such as Saatchi & Saatchi, TWB and many others. "The world's best shooters have terabytes of photos that never get used," he says. His service lets art directors and page designers specify exactly what they are looking for in a photo. Then it pushes those "image briefs" up to its network of photographers, who then match the spec to their extant images. And price their photos accordingly. "We offer an upgrade of the cliched stock shot," Moss said. "But not the luxury of the full commission brief. The client gets a $25,000 shot for $8,000 and the shooter gets 8K he would not have otherwise made." The critical value-add for Moss -- he gets a 30% cut on each photo sold through his service -- is that ImageBrief is not Flickr, Picasa, Dropbox or any sort of open content sharing platform. Rather, it's a carefully curated niche offering, and only vetted professional photographers and art directors can participate. When I asked him what his No. 1 marketing weapon is for connecting with roughly 5,600 photographers and 700 clients, Moss had a fascinating answer: It isn't Web marketing or social media or any sort of hip, big data analysis. Rather ... "It's dark social," he said. That is, the human interactions that happen in the digiosphere -- usually via Web chatter such as email, SMS or voice calls -- but not via big social networks. "You know they are there because the phone rings," Moss said. "But you can't measure it, so it stays dark."