Hello.
I'm trying to integrate miniBB and 4images. But i'm running into some problems.
i can't figure out what I have to change the cookies and one more problem is that 4images is using sessionID :/

Try to read this article:

https://www.minibb.com/synchronizing_minibb.html

I did.
miniBB is using 4images as it's userDB. But I still haven't figured out how I do the cookie and sessionID thing :(

Well, that's the most interesting part, and only you as a programmer can develop the custom script which parses/gets cookie information. Article mentioned describes how you need to that... actually miniBB needs to use the same authorization, as 4images.