nopCommerce comes integrated with reCAPTCHA that enables the store admin to enable CAPTCHA for list of specific pages in order to prevent spam on the website.
Before we go further into this tutorial, let talk about reCAPTCHA.
What is reCAPTCHA?
reCAPTCHA is a free service to protect your website from spam and abuse. reCAPTCHA uses an advanced risk analysis engine and adaptive CAPTCHAs to keep automated software from engaging in abusive activities on your site. It does this while letting your valid users pass through with ease.
reCAPTCHA offers more than just spam protection. Every time our CAPTCHAs are solved, that human effort helps digitize text, annotate images, and build machine learning datasets. This in turn helps preserve books, improve maps, and solve hard AI problems.
(Source: Google reCAPTCHA)