final NonCachingImage warningImage = new NonCachingImage("warningImage", new Model("images/alert_orange.png"));
warningImage.setOutputMarkupId(true);
add(warningImage);

----------------

  final AjaxLink link = new AjaxLink("theLink") {
            public void onClick(AjaxRequestTarget ajaxRequestTarget) {
                log.debug("Link Clicked...");

                warningImage.setModel(new Model("images/alert_green.png"));
                ajaxRequestTarget.addComponent(warningImage);
   }
        };
add(link);

---------------

INFO:
INFO: Initiating Ajax GET request on /1/meetmoi?x=YuQ6ay6aKBGDiO5OfiMmT7sqTYDzw7kvj2TxXBaK1HxBbP9XAjorn1Zpm4EovOnWCZVHg*4WCL-uPukV*-Oz2CeAsvJdoPkh&wicket:behaviorId=0&random=0.337860019529019
INFO: Invoking pre-call handler(s)...
INFO: Received ajax response (388 characters)
INFO:
<?xml version="1.0" encoding="UTF-8"?><ajax-response><component id="notYetActive_repeatingAlerts_1_aAlert_warningImage" ><![CDATA[<img id="notYetActive_repeatingAlerts_1_aAlert_warningImage" src="/1/meetmoi/resources/com.mdate.web.panels.alerts.MobileNotValidatedAlert/images/alert_orange_en_US.png?wicket:antiCache=1181744625859" wicket:id="warningImage"/>]]></component></ajax-response>
INFO: Response parsed. Now invoking steps...
INFO: Response processed successfully.
INFO: Invoking post-call handler(s)...