Screen Shot 2013-08-08 at 10.23.41 AMFrédéric della Faille and his three co-founders had spent six months working on their flagship product, Checkthis, an app that lets people share multiple photos within a single frame. It was supposed to be the Belgian startup’s big thing. As it turned out, however, it would soon be eclipsed by a side project cobbled together on the spur of the moment over the course of four weeks.

Today, the team behind Checkthis – two guys in Belgium, two in New York – are more excited about its new iPhone app, Frontback, which got 100,000 organic downloads in its first two weeks and, in the closing weeks of July, found its way into the top 10 for all iPhone apps in eight countries, and top 10 for photo and video apps in 35 countries.

Frontback is still a minimum viable product. All it does is let you take a photo of what’s in front of you and pair it with a photo of yourself (yes, a “selfie”), one on top of the other. Front photo plus back photo. It’s like Instagram with one extra level of context, and without the filters.

Della Faille, who used to be a graffiti artist before moving into Web design, started Checkthis as a company a year and a half ago. [Disclosure: Frontback and PandoDaily share an investor in common: Lerer Ventures.] He got the idea for Frontback by combining a selfie with a landscape shot to prove, as a use case for Checkthis, that two pictures can sometimes be better than one. His friends on the network liked the results and started doing their own. So he thought he’d build an app especially for the purpose, just to see how it worked out.

In creating the app, della Faille drew inspiration from both Vine and Snapchat, which allow people to easily create videos and images within specific constraints while providing ample room for creative expression. “That’s what we wanted to do with Frontback – create a medium,” della Faille says. “We wanted to have people creating and playing with the constraints.”

In the few weeks that Frontback has been around, its users have already produced works that intrigue, delight, amuse, and shock. Della Faille says the results run the gamut, from pastoral to sexual to familial. And, of course, there are a lot of cats, those anchor weights of the Internet.

Described in words, Frontback seems trivial and frivolous. So you can combine a front-camera shot with a back-camera shot: What’s the big deal? And, of course, in many cases there is no big deal. But at the same time, Frontback provides the opportunity for the creation and distribution of genuine art, even if it remains on the playful end of the spectrum. (See the slideshow of Frontback staff picks below for some examples.) Like Vine with its six-second loop and Snapchat with its scrawls and ephemerality, it allows a new form of storytelling that comes from the imposition of constraints as much as it does from the breaking down of production barriers.

This slideshow requires JavaScript.

That phenomenon, however, is an ancient one, stretching back to the earliest forms of art and literature. Classical Greece, for instance, invented the lipogram, which is a piece of writing that avoids using one or more letters. As the writers Wendy Walker and Tom La Farge point out, such a construction has been used to produce entire books, such as Georges Perec’s 1969 novel “A Void,” which runs 290 pages without using the letter “e.” Similarly, Gilbert Sorrentino published a novel in 2000, “Gold Fools,” made up entirely of questions.

The same “creativity from constraints” pattern can be seen in haikus (structured syllable counts), sonnets (14 lines and a strict rhyming structure), and collage (combination of multiple materials). The rule of limitations also applies to some of the best self-expression products on the Internet, including Twitter (140 characters), Instagram (square photos with filters), and Craig Mod’s new micropublishing venture, Hi (location and photo mandatory).

A 2011 study by social psychologists at the University of Amsterdam found that obstacles can open up our way of thinking. Through a series of experiments, as Wired pointed out, the researchers found that the imposition of an obstacle broadens one’s “perceptual scope,” meaning the struggle within constraint actually increased what people were able to notice. Simultaneously, however, those obstacles increased “conceptual scope,” which allows people to consider more ideas and possibilities. Here’s how the study’s authors put it:

Consistently, these studies show that encountering an obstacle in one task can elicit a more global, Gestalt-like processing style that automatically carries over to unrelated tasks, leading people to broaden their perception, open up mental categories, and improve at integrating seemingly unrelated concepts.

The accidental genius of Frontback is that it trades on this psychological effect while simultaneously unlocking the power of a smartphone matched to the Internet. Not only can people create little pieces of art, but they can produce them anywhere and share them instantly.

The app is still a couple of weeks away from having more social features added. For now, your feed on Frontback is populated only by staff picks. It is still a minimum viable product. There’s a fair chance, too, that it will just be a fad – a bit of fun that burns out as quickly as it took off.

Regardless, the Checkthis team is enjoying the ride. “The Frontback moment is something really strange and special,” says della Faille. He had never dreamt of a product that would allow the company to see the faces of its users. It is, he says, a “strange but positive feeling.”

In this particular form of storytelling, the face, unfiltered and unpretentious, is the caption, he says. The emphasis gets shifted away from the landscape and onto the point in time in which the event took place. That extra layer of context changed everything, says della Faille. “It’s really the moment that matters.”