Also, there's a (bit outdated) US Army report on crowdsourced geographic information. You'll find some basic methods/techniques. They summarize what you are looking for with relevant references to related literature. It's from 2012 though but it will get you started for sure.
Rice M T, Paez F I, Mulhollen A P, Shore B M and Caldwell D R 2012 Crowdsourced Geospatial Data: A report on the emerging phenomena of crowdsourced and user-generated geospatial data.