All users vote for the entry they like best.
Basically this:
There will be a sign up thread. Everyone who would like to join, can sign up there.
Then the participants send in their entries via PM. They are not allowed to say which entry is theirs, it's completely anonymous to prevent bias. There will be a poll where everyone can vote. Self-voting is allowed.
As for prizes, looks like
@Thururuzao has a plan there 👀.