Drupal’s captcha module allows site owners to add captcha (spam prevention) to variety of forms.
The captcha form placement is defined by the individual form ID and the module comes preconfigured to identify core form IDs.
However, the captcha module can also integrate with other webform modules such as the popular Webform module.
To manually add captcha to a Webform form, first you will need to find the Webform’s ID.
You can then copy and paste the form ID in the captcha Form ID box and select the type of challenge you want to apply to the Webform.