Instagram, the photo-sharing app owned by Facebook Inc. , is worth $35 billion, almost double its previous valuation, according to an analyst. The photo-sharing network recently announced it had surpassed 300 million active users, and has taken steps toward cleaning up spam accounts, as well as adding new filters and features in an update this week. In April 2012, Instagram, then only two years old, was acquired by Facebook for $1 billion. It only served around 30 million people and it had only recently extended its service beyond the iPhone. But on the first day the Android version hit, the app was downloaded over a million times, and its growth has continued apace. Over the past nine months, Instagram’s user base grew 50 percent, while Twitter’s active users grew by only 4.8 percent in the last quarter. Though Facebook has only recently introduced ads on Instagram, the Citigroup analysts believe the app could soon be a meaningful contributor to Facebook revenue. If Instagram delivers, then it's going to make Zuckerberg's $1 billion purchase of Instagram look like the greatest steal in the history of business. Between WhatsApp, Oculus and IG, Facebook's major acquisitions are worth $56B. That's more than the combined market caps of Twitter and LinkedIn.