This is the result of spending about a week making a copy of Flickr.com. Not all of the functionality is here, obviously.
So, what does this do? You can read more about this, or you can go play with it on heroku: http://flickrclone.herokuapp.com/
If users are going to do anything at all on the site, and have it associated with them, they'll need an account. Even though this is only a demo project, I wanted to work with supporting pseudonymity and anonymity. With this goal in mind, users can sign up with or without an email address. Also, it's not required that a user creates an account at all - more on that later...
A signed in user can upload one photo at a time. When choosing a photo, the user can add a title and description. They can also add this photo to an existing album or a group. When uploading as an anonymous user, a you can choose groups from a list of groups that allow posts by non-members.
A signed in user can create photo albums. A list of these is accessible from the user's page. An album's page shows all the photos currently in that album. On a photo's page, there's an option to add or remove that photo from albums.
When creating or editing a group, the user can specify if non-members are allowed to post to the group. When this option is selected, anonymous members can add photos. On a photo's page, the user (anonymous or signed in) can add the photo to a group. The list is filtered by what groups the user is allowed to post to.
When viewing other user's pages, the current user can add them as a friend. The photostream for contacts shows the most recent 3 photos for each contact.
If I continue working on this, I'll work on the problem of anonymizing photos. Step 1 is to make sure EXIF data is removed. Step 2 is harder - process the images such that the camera can't be identified by its sensor noise fingerprint (google 'sensor noise fingerprint' if you'd like to be upset). I haven't found good information on how to do this. It's an interesting problem, but was beyond the scope of a week long project.