Photo sharing app Instagram has overtaken Twitter for the first time. Across mobile phones in the US during August, Instagram received an average of 7.3 million daily visitors, while Twitter attracted 6.9 million users, a new report by ComScore said. It also found users spent more time on the photo-sharing site than those who visited Twitter. Instagram visitors spent an average of 257 minutes on the site via mobile phones in August, while those logging on to Twitter spent an average of 170 minutes viewing the site. The news is likely to be warmly received Facebook, which increasingly competing with twitter for the lucrative mobile market.