code: protected Image newImage(final String id, final IModel<CaptchaModelBean> model)
  	{
  		return newImage(id, model.getObject().getCaptchaImageResource());
  	}
docs: Factory method for creating a new {@link Image}. This method is invoked in the constructor
  from the derived classes and can be overridden so users can provide their own version of a
  Button.
  
  @param id
  the wicket id
  @param model
  the model.
  @return the new {@link Image}