Thanks to Nikolay I found out about something that was here (in s9y) for some time. (shame on me)
Automattic Kismet (Akismet for short) is a collaborative effort to make comment and trackback spam a non-issue and restore innocence to blogging, so you never have to worry about spam again.
In order to use it for your personal blog, you need wordpress registration ( :-O WHY? ), and after that to enter your API key into spam configuration of your s9y
I have removed the captcha plugin, and you can comment more easily 🙂