I am creating a website that involves posting service project listings online, and I want to require that all organizations posting projects are verified as either 501(c)(3) or government run organizations such as state parks (Are these 501(c)(3) as well? What would you call them?). How can they prove this?
A scanned document can be Photoshopped easily, so I don't think that would be the way to go. I thought perhaps if they verified their email as the same email that was posted on their website that would work, but not all nonprofits have a contact email or even a website.
This is a necessity of my site because it would be connecting people and organizations in real-life (offline) and I want to make sure that the organizations are who they say they are.
Also, is there a national official database of such organizations? It might help for verification as well as for filling in information.