Rick Webb, Tumblr's consultant on marketing and revenue, says that one of the keys to the social network's advertising strategy is that most people simply don't know about it.

"We have people say don't ever advertise," Webb said, "which we already are ..."

Tumblr, which gets 20 billion pageviews a month, began selling ad units on Tumblr Radar and Spotlight this spring.

Even though big advertisers like Adidas and Coke take advantage of the platform, most Tumblr users don't necessarily realize that what they're seeing are paid for posts.

"It's not in your stream, not in display ads," Webb continued at Business Insider's IGNITION conference.

The thing is, many brands were already taking advantage of Tumblr before it had paid advertising. The Hunger Games, for example, created a highly successful fashion blog called "Capitol Couture" that featured outfits from the movie's dystopic society.

Webb pointed out that this was all free and an example of the type of marketing content that does well on Tumblr: "The ones that emotionally move people."

Webb continued that for the most part, "I think a lot of photo sharing sites never tried to monetize through advertising."

While Facebook is the largest photo sharing site that's put its hat in the ring, other sites like Flickr didn't even try.

"I don't think it will be impossible for us," he said.