The new account has gained this massive following without the official help of Twitter, which often sticks celebrity and media accounts on its recommended-follow list, inflating their numbers.

As impressively, my analysis of 100 tweets from the account this week found that, on average, a @HistoryInPics tweet gets retweeted more than 1,600 times and favorited 1,800 times.

For comparison, Vanity Fair's Twitter account—with 1.3 million followers—tends to get a dozen or two retweets and favorites on any given tweet.

I've got about 140,000 followers and I've tweeted more than 30,000 times. I can't remember ever having a single tweet get retweeted or favorited as much as the average @HistoryInPics tweet.

Actual people seem to follow these accounts. A quick check on a tool that scans Twitter accounts for bot followers says that only five percent of @HistoryInPics' followers are bots. That's an incredible low number for such a large follower base. (For comparison, the tool found that 34 percent of my followers were bots.)

Qualitatively, looking through who follows @HistoryInPics, I don't see the telltale signs of bots. Famous people follow the accounts, too. Jack Dorsey famous. Kim Kardashian famous. (From his personal twitter account, @GirlsGoneKyle, Cameron recently posted a screenshot of a direct message that Kardashian sent to them.)

Even other media people—who, as we'll soon see, have big issues with the brand—just can't help themselves sometimes from sharing photos from the account, when the perfect image from the past crosses their feed at just the right moment. Who can resist Tupac Shakur on a stretcher, right after being shot, with a middle finger in the air? Or a World War I train taking soldiers through Flanders? Or Audrey Hepburn and Grace Kelley backstage at the Oscars?

In other words, @HistoryInPics is a genuine phenomenon built entirely on Twitter.

But strangely, in a world where every social media user seems to be trying to drive attention to some website or project or media brand, @HistoryInPics doesn't list its creators nor does it even have a link in its bio. There are no attempts at making money off the obvious popularity of the account. On initial inspection, the account looks created, perhaps, by anonymous lovers of history.

But no, @HistoryInPics is the creation of two teenagers whose closest physical connection is that they both live near the Pacific Ocean.

It's not just @HistoryInPics, either. They're also behind @EarthPix, which has similarly staggering stats, and several comedy accounts that they're in the process of selling that I agreed not to disclose. They've got at least five accounts with hundreds of thousands of followers and engagement metrics that any media company would kill for right now.

How do they do it? Once they had one account with some followers, they used it to promote other ones that could capitalize on trends they saw in social-media sharing. "We normally identify trends (or create them haha). We then turn them into a Twitter account," Di Petta said in an IM conversation. "Share them on established pages, and after 50,000 - 100,000 followers they've gained enough momentum to become 'viral' without further promotion."