Instagram that I think gets overlooked by students and teachers is that by Instagramming you're building a library of pictures that you own and can re-use whenever and wherever you want. I find that since I installed Instagram on my phone in 2012 I've taken pictures far more often than I ever did before installing it. These pictures often end up in blog posts and presentations.
Applications for Education
Instagram supports hashtags just like Twitter does. If you want to build a library of pictures with your students ask them to use a hashtag that you all agree to use to share pictures that can be re-used during the course of the semester or year. By doing this you and your students will build a gallery of b-roll pictures and videos. And if Instagram doesn't appeal to you, consider creating some of the other methods I've shared for creating a shared media gallery.