First make it your Image tag as itemRenderer like this
<s:GridColumn headerText="Employee" id="imageColumn" dataField="imageData" itemRenderer="components.GridItemRender"/>
And the GridItemRender.MXML
<fx:Script>
<![CDATA[
import mx.events.FlexEvent;
protected function emp_renderHandler(event:Event):void
{
if (data.imageData == null)
{
image.source = "http://localhost/demo/images/male.jpg";
}
}
]]>
</fx:Script>
<s:Image id="image" source="{data.imageData}" width="80" height="100" render="emp_renderHandler(event)"/>
I think this code may help you...