I'll only answer since this has been suggested several times before.
The biggest issue behind the quiz is that it's not just for stopping spammers, but people who have no malicious intent toward the site, but still don't bother to read the rules. Even if you were to make a quiz specifically revolving around the site's rules, people really aren't going to be answering correctly until they simply get enough experience with the site. The point restriction makes it so that we can easily catch posts that shouldn't be allowed.
The majority of the content in the admin pool ends up getting hidden, so to have a streamlined way to get people off that list without them knowing what posts are and are not allowed would do more harm than good.
Also, a lot of the spam accounts and stupid people that get kicked off aren't necessarily just a program, so it's not a difficult task to copy the suggested image for the quiz and do a google image search even if they didn't know what pokemon it was. Plus, this being a pokemon site, there's nothing stopping them from using our own site to bypass our own restrictions.