Adding reCAPTCHA to a WordPress site is fairly straightforward these days, however you may wish to add a spam prevention measure to a standard html form.

To use reCAPTCHA, you need a Google account. Sign into the reCAPTCHA admin console:

https://www.google.com/recaptcha

Register the web address your form is on.

This will provide you with a ‘site’ key and a ‘secret’ key.

Go to your web site mail form and add the code in the following places:

Form header

Prior to the submit button

On the mail processing form add the following code:

Note the positions where the site key and secret key need to go.

That’s it!