Oct 19, 2012 · 1 minute

Kevin Systrom says that he knew from day one that Instagram would be a big company. At PandoMonthly in San Francisco tonight, the Instagram founder told Sarah Lacy that he remembers looking at a team member on the photo-sharing service's first day and saying, "I think this is going to be big."

Systrom's startup had just pivoted from Burbn, a check-in app that failed to take off, and shifted to a service that focused on little square photographs. "Frankly, I was probably guessing," he said, recalling his sense of confidence about the company's prospects, "but I have never seen anyone fall in love so quickly."

The app got 25,000 users on its first day. "We just hit all of the right elements all at the right time," he said. From then on, the Instagram team focused on just making the app better, adding hashtags, new filters, and improving browsing. "We just put fuel behind it," Systrom said.

Systrom credits the power of network effects for helping the app's popularity to spread in the face of competition from other photo apps, including PicPlz, which was also funded -- and, for a time favored -- by VC firm Andreessen Horowitz. Most other photo-sharing startups were protective of their data and wanted to restrict users to keeping photos in their own environments. "One of the most amazing things about Instagram is you can take a photo on one network and share it to all of your networks at once," Systrom said. Even today, a quarter of photos shared on Instagram are also shared to Facebook or Twitter.

Systrom also said he doesn't think of Instagram as a photography company. "At the end of the day, we're a communications company. We're a messaging company. It's just that the medium in which that messaging lives is a photo."

One day, everyone in the world will own a smartphone, and every one of those smartphones will have a decent camera, he said. People will be taking photos all the time. "We want to be the network that takes those images that you're going to take anyway and broadcast those to people who really care about them."

[youtube http://www.youtube.com/watch?v=bhdNIs5Ymno&w=560&h=315]