Instagram, the photo-sharing service owned by Facebook, could be worth a whopping $35 billion, according to a new estimate by a Wall Street analyst. Citi’s Mark May issued a new valuation estimate for the popular app, far above the bank’s prior $19 billion valuation, a loftier view on the asset that May attributed to Instagram’s announcement last week that it had reached more than 300 million total users. “While Instagram is still early in monetizing its audience and data assets and its financial contribution to Facebook is minimal today, we believe that it is quickly gaining monetization traction and would contribute more than $2 billion in high-margin revenue at current user and engagement levels if fully monetized,” May wrote in a research report. The sky-high valuation makes Facebook’s 2012 acquisition of Instagram look like a slam-dunk.