Omid Cohensedgh, 19, a stu­dent at Colum­bia Col­lege, said his fin­sta­gram gives him an online plat­form for shar­ing inside jokes with a group of 25 peo­ple. “Me and my room­mate have these posters of Drake on our wall, and it’s an inside joke that we’re obsessed with him,” Mr. Cohensedgh said. “I wouldn’t feel com­fort­able shar­ing pho­tos of them with peo­ple who might not get it.”