<?xml version="1.0"?>

<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">

    <mx:Script>
        <![CDATA[
            public function initImage():void {
              image1.load("********image url*************");
            }
        ]]>
    </mx:Script>

    <mx:VBox id="vbox0" 
        width="600" height="600">
        <mx:Canvas>
            <mx:ProgressBar width="200" source="image1"/>
        </mx:Canvas>
        <mx:Button id="myButton" 
            label="Show" 
            click="initImage();"/>
        <mx:Image id="image1" 
            height="600" width="600" 
            autoLoad="false" 
            visible="true"/> 
    </mx:VBox>
</mx:Application>