Implementing a CAPTCHA on user forms using an online service

A common security measure on website forms is to use CAPTCHA codes. These codes use distorted letters or some other form of test to check that the person submitting data is not a spam robot. The form that we have been building to accept visitor-submitted book reviews could benefit from this type of technology to avoid weeding through unwanted entries.

This recipe shows how to integrate Google's reCAPTCHA service in our book review submission form. If you prefer using a local CAPTCHA script to avoid being dependent on an online service or to be sure that your form can be used around the globe, jump to the next recipe, Using a local library to implement a CAPTCHA on user forms.

Getting ready

You should be running the final version of the Book Reviews plugin created in Chapter 4, The Power of Custom Post Types, and should have already followed the Sending email notifications upon new submissions recipe. Alternatively...