Cultivating a classroom community where substantive discussions like this can happen is challenging work -- it's an ongoing process that takes time. But online discussion activities are one great way to give your students a leg up; use them as scaffolding for the "real" thing. Plus, the ability to engage in online discourse responsibly is a great 21st-century skill in and of itself.
ThingLink lets users add interactive links to any photo and turn them into fun web experiences that drive engagement.
An example is in the blog Classrooms 130 miles Apart Collaborating http://bit.ly/1QBVggm