ScolaCaptcha

As of version 3 of the reCaptcha, adding this functionality to your website makes the logo of Google appear on all pages of your website.
The plugin loads 2.5 seconds after the page has loaded. This is because we need to give Contactform 7 time to show its form.

The plugin will work on most WordPress installations, there’s hardly any php code, so hardly any server requirements.
At this point in time it does require jQuery, which is handled automatically.