There has been quite a number of spammers posting here. And they seem quite easy to arrest.
Why not consider using Google's captcha/re-captcha? It is actually stateful and if it determines one to be a human, the captcha simply requires a checkbox tick to proceed.
In contrast, every new discussion here requires answering a programming question, even for modifications...
I tried many times in incognito mode, the recaptcha is showing at the bottom right... it does not always prompt for verification challenge as i believed it is using invisible mode...