Hi Philip, this wouldn't be very related to your question, but I've been recently pointed to the idea of user notifications; e.g. when user passes by a building (for instance a monument) for which we have geocoordinates but no picture, s/he might receive a notification from the app to take a photo.
This was originally thought as a feature for the WLM app, but it might be useful for another purposes, too (for instance, for buildings which are not monuments, etc.).