WordPress.org

To install in regular WordPress:

1. Upload the wp-recaptcha folder to the /wp-content/plugins/ directory
2. Activate the plugin through the Plugins menu in WordPress
3. Get the reCAPTCHA keys here and/or the MailHide keys here

To install in WordPress MU (Optional Activation by Users):

1. Follow the instructions for regular WordPress above

To install in WordPress MU (Forced Activation/Site-Wide):

1. Upload the wp-recaptcha folder to the /wp-content/mu-plugins directory
2. Move the wp-recaptcha.php file out of the wp-recaptcha folder so that it is in /wp-content/mu-plugins
3. Now you should have /wp-content/mu-plugins/wp-recaptcha.php and /wp-content/mu-plugins/wp-recaptcha/
4. Go to the administrator menu and then go to Site Admin > reCAPTCHA
5. Get the reCAPTCHA keys here and/or the MailHide keys here