WordPress: Configure Captcha for Contact Form 7 Wordpress plugin

By far, Contact Form 7 could be the most popular contact plugin for WordPress platform. If we check the plugin's page, there are lot installs and really positive reviews. If you are looking for a contact form plugin, get Contact Form 7. I am also using the same for all websites done for clients on WordPress platform. 

Contact Form 7 can manage multiple contact forms, plus you can customize the form and the mail contents flexibly with simple markup. The form supports Ajax-powered submitting, CAPTCHA, Akismet spam filtering and so on.
- From Contact Form 7 Page