How to Ajax refresh captcha image (a image backed by DynamicImageResource)?

[Matthew Young]

I want to be able to show a new captcha image via an AjaxFallbackLink.  But
I don't know what to do in onClick to make the captcha img tag reload.

public MyPage extends WebPage {

     private CaptchaImageResouce captchaImageResource;

     public MyPage() {

        add(new Image("captchaImg", new PropertyModel(this,
"captchaImageResource")) {
            private static final long serialVersionUID = 1L;
            @Override protected void onBeforeRender() {
                regenerateCaptcha();            // make a new image
                super.onBeforeRender();
            }
        }.setOutputMarkupId(true));

       add(new AjaxFallbackLink("link") {
            @Override public void onClick(AjaxRequestTarget target) {

                // WHAT DO I DO HERE? Is there some javascript to make the
img tag reload?
                if (target != null) {
                    target.addComonent(MyPage.this.get("captchaImg"));   //
This is not enough to make it show
                }
            }

        }
    }


    public void regenerateCaptcha() {
        captchaResource = new CaptchaImageResource(randomString(3, 5));
    }
}