Why Instagram?

Of all the countless apps that allow users to share photos online, why did Instagram become such a huge fad, downloaded 30 million times since it was launched in October 2010? Why did Facebook Inc. choose to buy Instagram over any other, paying $1 billion for the Silicon Valley start-up last week?

Although the personal connection may have helped - Facebook cofounder Mark Zuckerberg once tried to hire Instagram cofounder Kevin Systrom - Instagram’s remarkable popularity likely did the most to bring about its billion-dollar payday.

The app is fun and easy to use; but so are other online photo-sharing services, like Path and Pixable. But only Instagram has racked up as many users so quickly. Instagram attracted 10 million users in its first year even though until last month, it was available only for Apple Inc.’s iPhone. When a version was finally released for Android devices two weeks ago, 5 million copies were downloaded in just six days.

Facebook declined to comment on the acquisition beyond official releases, and Instagram did not return a request for an interview. But Instagram’s slate of simple tools, called filters, for making an image sharper or prettier is clearly part of its unique appeal. The resulting image can be quickly snapped to family or friends. And Instagram allows users to publish their favorite shots online, even at other social sites like Twitter.

Jennifer Linde, a graduate student and mother in Carver, learned about Instagram from a cousin last summer. “I fell in love with Instagram simply due to the filters,’’ Linde wrote in an e-mail. “My photos are instantly turned into bright, crisp, fun portrayals of my life, instantly available to share with others.’’