Instagram co-founders Kevin Systrom and Mike Krieger are resigning amid reports of rising tension with parent company Facebook, a decision that ends their six-year relationship with the social media giant and fuels speculation about the future of the popular photo-sharing app. The founders sold their fledging app to Facebook in 2012 for nearly $1 billion and stayed on — Systrom as chief executive and Krieger as chief technical officer — while Facebook transformed the platform into a mega-success and one of its main sources of advertising revenue. According to Bloomberg News, Instagram grew from 30 million registered users when it was acquired to one billion monthly users in 2018. The media outlet in June estimated Instagram’s worth at more than $100 billion. While Systrom, 34, and Krieger, 32, have not commented publicly on their reasons for leaving, they said in a statement that want to take some time off and regroup.…