After just three months in the App Store, photo app Instagram has reached 1 million registered users, the company announced Tuesday.

"We believe it's the beginning of something bigger," Instagram said in a blog post.

Instagram debuted in October, and lets users add 11 different custom filters to photos in order to change the colors, mood, border, and tonality of their snapshots.

"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."

The app hit the App Store at 12:15am on October 6, and within a few minutes, people "started signing up in droves," Instagram said. Employees rushed to the office to add capacity to the service.

"It was both rewarding and humbling to see people embrace Instagram as both a new home on their iPhone - and a new way of communicating visually with people around the world," Instagram said. "We believe this is only the beginning. With 6.7 billion people in the world, we're a tiny fraction of the way there, but we're extremely happy with the progress."

The news comes one day after Foursquare unveiled a revamped iPhone app, which allows photos pushed to Foursquare from Instagram to be check-ins with photos instead of just check-ins. Earlier this month, Twitter announced several new media partners that will allow their products to be viewable via the "new Twitter" preview panes, including Instagram. Now, users can look at their Instagram photos right in the Twitter stream.