It's free, but so far is only available as a mobile app for iOS or Android. (The resolution of individual pics is also limited and as you can see it watermarks each one.)

Even though it's a sever-side application, there doesn't seem to be a web interface yet. At a guess, I'd say that this may be because running the client as a mobile app means that all the handling of uploading and downloading images can be delegated to the mobile device the app is running on, rather than having to create and handle an account for each user. However, I do hope they open it up - from the results I've seen, I'd be prepared to shell out a few quid for a version that worked with high-res images from the desktop.