Recently I was contacted by an individual who I have done some Drupal work for in the past. He has an older site that is primarily static HTML with a perl script handling contact form submissions. As most of us experience once a website has become established, he was getting inundated with spam through his contact form.
He was willing - though not overly eager - to implement a CAPTCHA solution but was worried about introducing an extra hurdle for those making casual inquiries. As the various spambots were filling in all the form fields with mostly random garbage and their website links, we decided to just do a validation on the phone number textarea and reject the submission if the phone number validation failed.
Read on for a sample implementation of 'reverse CAPTCHA' aka 'negative CAPTCHA' as an extension to the existing Drupal CAPTCHA module.
