The 150 million photos figure amounts to 1.3 million photos uploaded per day or 15 photos posted per second.
"The growth of photos being posted per day is tracking on an exponential curve," Instagram CEO and co-founder Kevin Systrom tells Mashable. "It's the one curve we look at to measure the health of the service and the addiction of the product."
For Systrom, Instagram's instant and continued success has allowed it to become a social network -- not just a mobile application -- where photography doubles as a form of communication.
"We're one of the fastest growing social networks in mobile -- having remained in the top 25 free apps in the App Store for over a month now," he says. "Where mobile apps come and go, Instagram has continued to see unprecedented growth in users and usage."
Instagram remains an iPhone-only application, though the startup's API has allowed third-party developers to bring pieces of the Instagram experience to other platforms. An Instagram application for Android, which has been promised since day one, is still on the road map -- but the company isn't saying anything about when you can expect it.
Image courtesy of Instagram, @Kevin
Instagram's Top Photographers
In late June, Mashable compiled a gallery of photos, tips and tricks from the service's most-followed users, as seen below.