The idea is quite simple.
InstaChallenge is a service to host and manage Instagram photo challenges. Everyone with an Instagram account is invited to hold a challenge and manage submissions and voting with the help of this website. Participiants can submit their pictures by tagging them or by selecting from their streams. In both cases it is necessary to register and allow InstaChallenge to access the streams (read-only, of course).
InstaChallenge.com enables you to have a jury to rate the images. This even works with many jury members from all over the world. You can easily invite jury members by their IG usernames.
Finished challenges may result in a (printed!) photo book (see below), e-books or other formats. The registration principle ensures that all copyrights are preserved and that individual rules of each challenge are accepted, esp. the use of hastags.
The following photobooks have already been published: