He first crept into the public consciousness when a 2012 Gawker story about his being banned from Instagram went viral. (He got the boot after posting a picture of topless women sunbathing at Fort Tilden Beach.) Today, Daniel Arnold is back on the social-media platform, where he shares a steady stream of photos, and has published a monograph—Pickpocket—but hasn’t changed much otherwise. He is the street photographer of the moment.