Mark is looking for an alternative to Facebook. Leo says that he's quit Facebook once and he thinks they're very manipulative in how they manage his feed. So he understands why he would want to leave. He's also noticed that the more time he spends on social media, the worse he feels. It's a time suck. For photo sharing, Flickr is a good site, as is 500PX.com is another. Instagram has a lot of the best of Facebook, but it's owned by Facebook. Think of it as "Facebook lite."
There's a Facebook clone called Diaspora, but Leo says he doesn't know the fate of it lately. He could also run it on his own server.