<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/06/29/preventing-an-image-from-automatically-loading-in-an-image-control-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white"
        initialize="init();">

    <mx:Script>
        <![CDATA[
            import mx.containers.ApplicationControlBar;
            import mx.controls.Button;
            import mx.controls.Image;

            private var btn:Button;
            private var img:Image;

            private function init():void {
                btn = new Button();
                btn.label = "Load Image";
                btn.addEventListener(MouseEvent.CLICK, btn_click);

                var appControlBar:ApplicationControlBar = new ApplicationControlBar();
                appControlBar.dock = true;
                appControlBar.addChild(btn);
                Application.application.addChildAt(appControlBar, 0);

                img = new Image();
                img.autoLoad = false;
                img.source = "assets/Fx.png";
                img.maintainAspectRatio = true;
                img.percentWidth = 100;
                img.percentHeight = 100;
                addChild(img);
            }

            private function btn_click(evt:MouseEvent):void {
                img.load();
            }
        ]]>
    </mx:Script>

</mx:Application>