Would anyone of you guys use it?
Any ideas on how to let users add this data without getting loads of duplicates. I know that it will change as it evolves but I want to at least get it off to a stable start.
You've got a centralised database recording input from users behind this all right?
Could you start by populating it with as much information as possible to begin with?
List as many walls as you can, and the boards within them. These two at least will be fairly immutable, so you can reduce/avoid duplication at this level.
The sets vary on a given board, so that'll be trickier to avoid duplicates, e.g. one person might enter "July re-set of 40 degree board" another might enter "July 40 degree set". You might be able to apply fuzzy matching to identify if a new set already exists. Alternatively you might try using the date for a given wall/board and if someone tries to upload a new set on an existing wall/board they are presented with the existing ones first to check whether the set already exists. At this point you can rely on the user not to duplicate, or you might try some fancy image comparison software to see if the picture they take and upload is of the same thing (something along the lines of a neural net, like Googles DeepMind or Udacity), but that doesn't guarantee success.
Alternatively you could contact walls or people who set at walls and ask them to upload pictures when the wall is set and limit users in this manner. Might hinder uptake/usage of your application though.
The issue here is mainly getting good pictures of the current set on a given board. It has to be users that keep it up to date or it will be super limited. I go to 2 walls so thats not really much use!