This is a fantastic component. Like all the CAPTCHA based components it requires some modifications to the Joomla core files. This is a necessary evil I'm afraid and those who complain that it's too complex dont understand this.
In addition to be an excellent component on it's own, the developer has provided information to other developers on how to integrate it with other components. This means that VirtueMart 1.1.3 comes with support for Security Images 5 already baked in.
Well done! Great component.