Professional version 2.6.0 of the plugin has introduced Google Recaptcha version 2. This is an easier and safer captcha, than the previously one used (Google Recaptcha version 1). Google Recaptcha version 2 is the default captcha selected, however you need to define site and secret keys for your domain in the plugin's settings from Google Recaptcha website. To do this, you need to have a Google account. If you do not have a Google account, then you can use the alternative Google Recaptcha version 2 captcha, which does not require any keys or accounts, by setting captchatype="RecaptchaV2 (no account)" in your shortcode. Please note that this feature may not work in all cases. For backward compatibility you can still use Google Recaptcha version 1 captcha, by setting captchatype="RecaptchaV1" in your shortcode.