Requested by Brian
Make an option in Control Panel under Server Administration to switch Captcha systems.
Currently captcha uses SimpleCaptcha by default. READ http://www.liferay.com/community/forums/-/message_boards/message/5430411 << THAT POST.
It has all the settings for captchas in portal-ext.properties. Normally, a user needs to go into that and add those properties.
Only TWO need to be configured by the user: they are the public and private keys for recaptcha's service.