How to integrate captcha to multi page webform
One thing that may work is altering the form using HOOK_form_alter() and than modifying the form to show the captcha only on the last step something as below:

/**
 * Implements hook_form_alter().
 */
function MYMODULE_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  // Get the form id through dpm() or print_r().
  switch ($form_id) {
    // Add the form id as here.
    case 'webform_client_form_form-id':
      // Get the value of step number and the total number of steps in form.
      $page_num = $form['details']['page_num']['#value'];
      $page_count = $form['details']['page_count']['#value'];

      // Check if its not the last step and catcha present in form.
      if (($page_num != $page_count) &amp;&amp; (!empty($form['captcha']))) {
        // Remove the captacha from the form.
        unset($form['captcha']);
      }
    break;
  }
}