Alternative option for "reCpatcha from Google"
CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart. (Yes, it really should be “CAPTTTCHA.” Don’t blame us; we’re not the ones who made up the term.) It’s a type of challenge test used on web sites to verify that the transaction taking place—the comment being posted, the account being registered, the vote being cast in a poll—is coming from a human and not a computer program. In addition to the examples mentioned above, CAPTCHA are used to block registration spam and contact form spam, to prevent scrapers from stealing email addresses and search bots from accessing private data, to deter dictionary password search attacks, and to preempt servers from getting bogged down by spam and malicious scripts.

Using Captcha may reduce spam but it would also reduce real comments/posts drastically 🙁

Something to notice:
CAPTCHA will reduce your spam but it won't eliminate it. People are paid to decipher those glyphs. Some sites use the glyph that was presented to them for their own site so some hapless visitor will decipher it
The biggest problem with spam on sites is if you use software that's in widespread use (eg phpBB). Your best bet for those is to make enough modifications to defeat out-of-the-box scripting. You may get targeted anyway but spamming is a high-volume low-success game. There's no real reason to target your site until it accounts for a significant amount of traffic.

The other thing worth mentioning is techniques that can be used to defeat scripted spam:

 
After doing some Google research (search :D) I found Mollom or Akismet a better solution than any others. But I will enlist them all according to my preference:

 Check it’s pricing scheme. http://mollom.com/pricing
 

I was using Akismet for my wordpress blogs and found it very effective. It was free few years back but now it has some pricing schemes but it is worthy to use.
Check its planning scheme: https://akismet.com/signup/
 
To check which plugins and libraries this app supports: http://akismet.com/development/
 
It has almost all the features that mollom has except

 
We may go for Image captcha for following reasons:

 

As name suggests, it will check if you are a real human being or spam. Though it will not ensure 100% spam protection which no app does but It’s good, easy and fun to use & implement. Users will like too 😀
 
Please check the demo, you will smile for sure: http://areyouahuman.com/demo/
 
It works with HTML5, iPhone, Android, WordPress, Drupal plugins and PHP, Perl, Ruby, Python, .NET libraries. Here is the link: http://portal.areyouahuman.com/installation
 

Picatcha is an image-based CAPTCHA with the goal of making it easy for humans to read but harder for bots to crack. We can try this too.  Pricing scheme seems nominal too. Free, $5 and $10 per month schemes.
Check its comparison with text based captcha here: http://picatcha.com/captcha/
Picatcha related documents: http://picatcha.com/api/

 

This is also image based captcha solution implemented as an alternative to text captcha or reCaptcha mainly. There is nothing much to explain in it. Demo itself explains everything.
Confident CAPTCHA™ is a clickable, picture CAPTCHA that stops spam and bots on websites by asking visitors to click on specific pictures.
Pricing schemes not mentioned here. But we can do a free trial experiment on it 😀

Why to use:

 
Deployment Options