The nice thing about reCAPTCHA is that it’s got descent strength, and people are familiar with it due to the wide deployment.
Use reCAPTCH with WordPress simply requires installing the WP-reCAPTCHA plugin:
- Install via Administration -> Plugins -> Add New
- “Network Activate” the plugin (instead of just “Activate”)
- Config the plugin via Administration -> Super Admin -> reCAPTCHA – enter your API keys here; make sure to check reCAPTCHA for comments
- MailHide apparently also requires the PHP mcrypt module to be installed – make sure that’s the case via apt-get install php5-mcrypt
All of the network sites will now have reCAPTCHA enabled.