This feature provided by the security image addon allows you to add a "human verification" image within all form to cut down on "robo script use" within your site. This simply makes sure that a human is logging in or using the registration form. This feature can be added to the following features in the software:
This addon must first be installed and enabled in the following admin tool before it can be used on your site:
ADDONS > MANAGE ADDONS
And once you have that addon enabled you'll see the following admin tool to manage that feature:
ADDONS > SECURITY IMAGE > SETTINGS
Within that admin tool page you'll see the following:
Within that screenshot you'll see the location of that admin tool page and: