As detailed in a video on the official Instagram account of... Instagram, "Starting today, you can pinch to zoom on photos and videos in feed, on profiles and on Explore."
For now, the feature is limited to iOS devices, with a forthcoming update coming to Android in a few weeks. Somehow, as Mashable points out, IG has always lacked the basic image function included on iOS since 2007. For the record, IG was born in 2010. Other things that last six years: US Senate terms; the entirety of Dawson's Creek;
Kim Kardashian's marriages.