Tim is almost correct... You'll notice the form ID he mentioned uses hyphens (-), whereas the form IDs required by Captcha and Antibot use underscores (_).
The correct way to find a form ID for use with anti-spam modules is to look for the hidden input element in the form with name 'form_id'. The value of this element is what you want:
So in this case (for the comment form at the bottom of this Forum page) the form ID is: comment_node_forum_topic_form
In this case this form ID is different to the ID attribute on the form element itself, but generally they are the same (save for using hyphens vs. underscores).
Tim is almost correct... You'll notice the form ID he mentioned uses hyphens (-), whereas the form IDs required by Captcha and Antibot use underscores (_).
The correct way to find a form ID for use with anti-spam modules is to look for the hidden input element in the form with name 'form_id'. The value of this element is what you want:
So in this case (for the comment form at the bottom of this Forum page) the form ID is: comment_node_forum_topic_form
In this case this form ID is different to the ID attribute on the form element itself, but generally they are the same (save for using hyphens vs. underscores).