Dukescript simple accesible captcha

HelloViaKO.java

package dew.demo.clickcaptcha;

import net.java.html.json.Model;
import net.java.html.json.Property;
import net.java.html.json.Function;
import net.java.html.json.ComputedProperty;

@Model(targetId="", className="Captcha", properties={
     @Property(name = "clicks", type=int.class),
     @Property(name = "clicksEfectuados", type=int.class),
     @Property(name = "image", type=String.class),
     @Property(name = "alt", type=String.class)
 })
final class ClickCaptcha {
  @Function static void increaseCounter(Captcha datamodel){
    datamodel.setClicksEfectuados(datamodel.getClicksEfectuados()+1);
  }
  
  @Function static void send(Captcha datamodel){
    if(datamodel.getClicksEfectuados() == datamodel.getClicks()){
      datamodel.setImage("http://findicons.com/files/icons/684/vistoon/256/check.png");
      datamodel.setAlt("Captcha exitoso");
    }else{
      datamodel.setImage("https://cdn3.iconfinder.com/data/icons/musthave/256/Delete.png");
      datamodel.setAlt("Captcha fallido reintente por favor");
    }
  }
  
  @Function static void retry(Captcha datamodel){
    datamodel.setClicksEfectuados(0);
    datamodel.setClicks((int)(1+Math.round(Math.random()*21)));
    datamodel.setImage("");
    datamodel.setAlt("");
  }
  
  private String numberToString(int number){
    return "";
  }
  @ComputedProperty static String instructions(int clicks, int clicksEfectuados) {
            return "De click "+clicks+" veces exactamente para acceder. Usted ha dado "+clicksEfectuados+" clicks";
   }
  
  public static void main(String... args) {
    int result = (int)(1+Math.round(Math.random()*21));
     Captcha datamodel = new Captcha(result,0,"","");
     datamodel.applyBindings();
   }
  
}

index.html

<button class="btn" id="button" data-bind="text: instructions, click:increaseCounter"></button><br>
<button class="btn" id="send" data-bind="click:send">Acceder</button>
<img data-bind="attr: {'src' : $root.image, 'alt': $root.alt, 'height':20, 'width': 20}"></img>
<button class="btn" id="retry" data-bind="click:retry">Reintentar</button>