Naomi Zeichner interviewing Kevin Systrom, one of the founders of Instagram:

How did you develop the idea of the Instagram filter? It started off as a mobile check-in app that let you post pictures and videos. People ended up liking the photo posting more than the checking in, so we built in camera functionalities and made the focus photos, not check-ins.

One question Zeichner didn’t ask: how does Instagram plan to start making money?

Instagram Started as a Location Check-In Service