Earlier, it was questions. Then came reCAPTCHA, then I am not a robot. Now it is the time of Invisible CAPTCHA
There are also tools like stop forum spam, project honeypot and Akismet which works great on a variety of websites.
Which one do you ? How effective are they ?
Abhi these days, I prefer to steer clear of services such as reCaptcha as they are a privacy concern - even though Google won't admit it. Others such as Akismet are generally ok, but rely on passing your data through an API in order to determine if a message is spam or not. Again, another privacy issue.
My preferred approach is to leverage honey pots as these run on the site itself without the need to send data elsewhere for analysis.
Have you tried Q&A ? Do you think it will work now ?
Some people ask questions that requires expertise. Something that only niche topper will know.
Abhi simple math equations are common. These are easy for a human to solve, but not for any bot.
Something in regional language will be fun as well. But if the bot use Google Translate, then it is of no use.