It's not something that can be readily outsourced to "the crowd" in general but it is something that can achieved using a hierarchy of interested/invested self checking power users.

It's a similar problem to that faced by, say, open source projects that aim to maintain a certain level of code quality and style matching in contributed source code.

Addendum: the image collections of the Australian National Botanic Gardens and the Australian National Herbarium might be of interest to you down the track: http://www.anbg.gov.au/anbg/photo-collection/index.html