conflict between Drupal reCAPTCHA and profiles that enable user registration

If the Drupal reCAPTCA module is enabled on Drupal user registration forms, profiles with the 'user registration option' enabled will fail when the user attempts to create an account. This is due to the Drupal reCAPTCHA element being present in the user form that is submitted by CiviCRM programmatically. However, since this form element is not presented to the user, there is never a chance to enter a response.

Workarounds exist, but they involve the convoluted use of url rewriting to prevent access to the Drupal user registration page. This is a complex and error-prone process.

The simple fix is to remove the reCAPTCHA element from the Drupal form before submitting it. Note that the reCAPTCHA element is only removed for forms submitted by CiviCRM profiles programmatically. For such profiles, the CiviCRM reCAPTCHA element can be enabled.