Editor's Note: This article is part of a series that examines the lessons behind disruptive products through the lens of design.

Making the transition from startup to billion-dollar business in less than two years may sound impossible, but that’s exactly what happened with Instagram.

And though the photo app’s plentiful filters have helped cultivate a legion of loyal followers, you could call the company’s prime benefactor iteration itself. Instagram’s founders originally designed the app in 2009 as a more complex program called Burbn that combined elements of Foursquare and the popular Zynga game Mafia Wars. It was only after they stripped the app down to its core photo-sharing function in 2010 that Instagram found its footing.

Four years and 16 billion photos later, the app has disrupted social media and mobile photography faster than almost any other startup.

So how did Instagram founders Kevin Systrom and Mike Krieger sell their mobile app to Facebook for $1 billion without having generated a penny in revenue?

Here are four design tips that helped Instagram change photo-sharing forever:

1. Seamlessly solve a problem.

Before Instagram, photographs taken on mobile phones rarely looked polished and professional. The company’s roughly 20 different filters changed all that by letting users add colorful tints that lend a modern or retro feel to images. So not only could people suddenly edit their photos with professional tools, they felt like professional photographers too.

2. Prioritize convenience and sharability.

Instagram streamlined the sharing process by offering the ability to share photos instantly and on multiple platforms, such as Facebook, Flickr and Twitter. A newer feature called Instagram Direct lets you share content to specific users, up to 15 at a time. Instagram also makes it easy to upload and share photos not taken with the app.

3. Don’t stop designing new features.

Instagram’s founders may have landed their billion-dollar payday in 2012, but that didn’t stop the company from adding its most significant new feature more than a year later. Instagram’s video tool lets users post and share up to 15 seconds of footage--long enough to create something substantial but short enough to minimize download time.

With the added functionality came 13 new video-only filters and also the “Cinema” feature, which uses image stabilization technology to convert shaky, wobbly footage into professional-looking video that resembles footage shot with a Steadicam. This feature helps distinguish Instagram from similar camera apps like Vine that don’t offer image stabilization.

4. Stay true to your core audience.

One of the most unique characteristics specific to Instagram is how the online version of the service has fewer capabilities than the mobile version. While users can view their photo feeds through any web browser, posting to Instagram is only possible through a mobile device. By retaining the company’s mobile-only DNA, Instagram is able to keep its focus on that audience and build for it today and tomorrow.

What other design-centric companies do you admire?