When I post new topic, I've used BB Code: [url] [img] tags but it not works. It replace my links from http://www.domain.com/picture.jpg to http://www.domain.com/pi cture.jpg?
Why it does and how to resolve this problem?

Check this:

https://www.minibb.com/forums/9_4433_0.html

point #4 Good anti-spam update...

You need to make at least 5 postings before it happens. Else you're allowed to do that in the same rights as the spammers.

But we are thinking currently for disabling it for images at least.