Imgur started as a place to host photos posted to reddit. It would be interesting if Imgur surpassed Reddit, but they serve different purposes. Reddit is a link aggregator supported by community discussion. You may see a lot of photos, but you'll also see news and other interesting websites and conversations. I'm not super involved in the Imgur community; I know it's kind of taken off as its own thing. AFAIK, though, you don't post "TIL" or "ELI5"-style posts to Imgur.