Instagram was in the App Store for just three months before it gained a million users, and now just six weeks later, the iPhone app has doubled that number.
Launched in October, Instagram lets users add 11 different custom filters to photos in order to change the colors, mood, border, and tonality of their snapshots. The company tweeted Monday that it had reached the two million user milestone.
"When we started working on Instagram, we tried to imagine what the world would be like if everyone could contribute media to an open, transparent, and international community," the company said. "For a startup with 80 users at the time, this was a big hairy audacious goal. Little did we know that within a few short weeks we'd see more images from all over the world than we could have ever imagined."
Instagram also recently opened up its API to developers.
"Until now, users' data has only been accessible through our iPhone app. A big part of this was by design: the fundamental belief that choosing to focus our efforts on one thing, and doing that one thing well would help us iterate quickly and build what in four short months has gained nearly two million users," the company said in a blog post. "We feel that the first step to creating a lasting company is to work with the many talented developers out there in the world."
To put Instagram's growth in perspective, it took Twitter two years to gain a million users. It took a long time for the social-networking site to grow; although it now has about 200 million registered users, 95 percent of those accounts were created since January 2009.
Foursquare recently signed up its six millionth user. Launched March of 2009 it took the location-based service about a year to snag a million users. However, the company said in a recent blog post that its growth rate sped up in 2010, expanding by 3,400 percent.
Instagram reported that close to 300,000 photos are posted on the app each day, and the company just closed out a $7 million funding round led by Benchmark Capital.