As you'd expect, the cracking community is very close knit and cliquey. It's pretty tough to get into and there aren't really any worthwhile books on the subject. The only real way to learn is to join one of the guilds and become an apprentice to a master-cracker. There are a few ways to do this, all of which involve proving your that you have some talent in the area. You can search the internet to find other gateway tests (they're usually on websites that have been cracked), but there's one I know of
here. There's hidden information in the image, which will give you instructions on how you continue the initiation process. That's all I can tell you really, anybody is free to attempt the initiation, but I can't help you with it.