ext_photo = new URLLoader(new URLRequest(path)) // path - Путь к внешней фотке
ext_photo.dataFormat=URLLoaderDataFormat.BINARY
ext_photo.addEventListener(Event.COMPLETE, extLoaded)

private function extLoaded(e:Event):void { // Данные мы получили, теперь грузим их заново сами в себя!
    var loader:Loader = new Loader()
    loader.contentLoaderInfo.addEventListener(Event.COMPLETE, introReady)
    loader.loadBytes(ext_photo.data);
}

private function introReady (e:Event):void {
    var sourceData:DisplayObject = DisplayObject((e.target as LoaderInfo).content)
    // Собственно можно считывать параметры sourceData
}

loader.loadBytes(ext_photo.data, new LoaderContext(false, ApplicationDomain.currentDomain));

package
{
    import flash.display.*
    import flash.events.*
    import flash.net.*
    import flash.text.*;
    import flash.system.*
    
    
    /**
     * ...
     * @author chingachgoog@mail.ru
     */
    public class Main extends Sprite
    {        
        public function Main():void
        {
            if (stage) init();
            else addEventListener(Event.ADDED_TO_STAGE, init);
        }
        
        private var ext_photo:Loader
        private function init(e:Event = null):void
        {
            removeEventListener(Event.ADDED_TO_STAGE, init);
            // entry point
            ext_photo = new Loader()
            ext_photo.load(new URLRequest("http://upload.wikimedia.org/wikipedia/commons/a/aa/Kronung_Heinrich_II.jpg"))
            ext_photo.contentLoaderInfo.addEventListener(Event.COMPLETE, extLoaded)
            ext_photo.contentLoaderInfo.addEventListener(IOErrorEvent.IO_ERROR, toErr)
            ext_photo.contentLoaderInfo.addEventListener(SecurityErrorEvent.SECURITY_ERROR, toErr)
        }
        
        private function toErr(e:*):void {
            setText(e.toString())
        }
        
        private var loader:Loader
        private function extLoaded(e:Event):void { // Данные мы получили, теперь грузим их заново сами в себя!
            loader = new Loader()
            loader.contentLoaderInfo.addEventListener(Event.COMPLETE, introReady)
            loader.loadBytes(ext_photo.contentLoaderInfo.bytes);
            addChild(loader)
        }

        private function introReady (e:Event):void {
            var sourceData:DisplayObject = DisplayObject((e.target as LoaderInfo).content)
            // Собственно можно считывать параметры sourceData
            setText(sourceData.width+" "+sourceData.height)
        }
        
        private var tf:TextField
        private function setText(str:String):void {
            if (!tf) {
                tf = new TextField()
                tf.autoSize = TextFieldAutoSize.LEFT
                tf.wordWrap = true
                addChild(tf)
            }
            
            tf.appendText("\r\r"+str)
        }
        
    }
    
}