Heroku-hosted screenshot server
$ heroku create --stack cedar --buildpack http://github.com/stomita/heroku-buildpack-phantomjs.git
$ heroku config:set SECRET=<mysecret>
$ git push heroku master
$ curl http://myscreenshotapp.heroku.com/snap?url=http://www.google.com&auth=<mysecret>&postback=http://...