What is recaptcha and how/will it help prevent spam ?
For answers to those questions you can look at google's page about recaptcha(https://google.com/recaptcha)
This installation guide requires drupal 6,7 or preferably 8 (or higher).
Note this installation requires captcha and recaptcha, these are different plugins and not a type error.
- Extract the archives into sites/all/modules/[recaptcha/captcha]respectively and relative to your own drupal installation (this folder may need to be created manually)
- Now navigate to your drupal administration page in your browser (/admin/modules)
- Search for captcha and enable it
- Search for recaptcha and enable it
- Once complete it is advisable to configure your captcha setting in the web interface (/admin/config/people/captcha)