The popular photo sharing app Instagram, which allows users to capture photos or import them from a smartphone’s camera roll and then apply retro effects before sharing them with friends, is coming off its biggest month yet. After being acquired by Facebook for $ 1 billion dollars, the app amassed more than 5 million Android users a mere week after the service launched on Google’s operating system. Instagram continued to see tremendous gains, surpassing 10 million Android downloads and totaling 40 million users in late April. Mashable on Tuesday reported that Instagram now has more than 50 million users and, according to its API, is adding roughly 5 million per week. Instagram is free for both iOS and Android.