If you manage a website that allows anonymous posting, spam will always find you, soon or later. What's the easiest way to filter spams without doing chunk of work?

Deny by IP

location / { deny 124.XXX.XXX.XXX/24; deny 58.XXX.XXX.XXX/24; }
after I added that and reloaded the nginx, spam stopped.

Prior to this, I added captcha check for posting, but that didn't stop the spam at all. Because spam originates from Bangkok, thailand, I wonder if they hired those low cost laborer to send out spam manually, or at least semi-automatically. With ip deny trick, at least it works for now.

Reference

http://wiki.codemongers.com/NginxHttpAccessModule