Call back method to return the CAPTCHA text for registering the user.
public String validateCaptcha(String image){
//Show the image to the user.
//Get the Captcha text
return <captchaText>;
}
               
            Alternately, it can also return ‘null’ in which case, the captcha text has to be stored by the application and a subsequent registerUser(captchaText, isSynchronous) has to be explicitly called on
UserManager
.