```
drush dl captcha
```
Once the module is downloaded, enable it by navigating to "Modules" in the Drupal admin dashboard and checking the box next to "CAPTCHA" and its dependencies. Save the configuration to enable the module.
After enabling the module, you'll need to configure the CAPTCHA settings. Go to "Configuration" in the admin dashboard and select "CAPTCHA" under the "User Interface" section.
Here, you can set various options, such as the CAPTCHA type (e.g., image CAPTCHA or reCAPTCHA), the form(s) on which to display the CAPTCHA, and styling options.
If you choose to use reCAPTCHA as your CAPTCHA type, you'll need to obtain reCAPTCHA keys from the Google reCAPTCHA website. These keys will be required to integrate reCAPTCHA with your Drupal site.
If you're using reCAPTCHA, enter the obtained keys into the CAPTCHA settings page in your Drupal admin dashboard.
After configuring the CAPTCHA settings, make sure to test it thoroughly on your website's forms, such as user registration, login, or comment submission, to ensure it is working as expected and effectively preventing spam.
Please note that as Drupal 7 is no longer actively supported, it's essential to consider upgrading to a newer version of Drupal to ensure you receive security updates and the latest features. Drupal 9, for example, has significantly improved security and performance compared to Drupal 7. If you decide to upgrade, be sure to check for module compatibility and create a thorough backup of your website before proceeding with the migration.