Yeah this is something I've been thinking about recently, not so much in terms of the difficulty of managing spam on a per post basis, as I'm thinking that the instances will be very small and moderation on that front should be easy, so long as you can keep the problematic user from signing up in the first place. One thing I've been thinking is that perhaps there could be a captcha-like solution that will benefit from the limited location. For instance: Select only images that are of this location. Local users will know, bots will struggle. It doesn't stop anyone else from using Google street view or something but it does make the bar the bit higher. I don't know how to deal with the obvious accessibility issue with this though so I'm going to keep it in mind until I get around to that sort of thing. Long term of course we're going to have the issue with federated spam also, so I don't want to implement a solution that will only be in my way in the long run.