• the first one is a Bitmap
• the second on is a MovieClipLoaderAsset

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">
 
    <mx:Script>
        <![CDATA[
        	import mx.core.MovieClipLoaderAsset;
        	import mx.core.BitmapAsset;
            import mx.collections.ArrayCollection;
            
            [Embed(source="placeholder.swf")]
			private const ARTWORK_PLACE_HOLDER_SWF:Class;
			
			[Embed(source="placeholder.png")]
			private const ARTWORK_PLACE_HOLDER_PNG:Class;
 
            [Bindable]
            private var collection:ArrayCollection = new ArrayCollection();
 			
 			private function handleImage(e:Event):void{
 				
 				if(e.currentTarget.selectedValue == "PNG"){
 					
 					img.source = ARTWORK_PLACE_HOLDER_PNG;
 					
 				}else{
 					
 					img.source = ARTWORK_PLACE_HOLDER_SWF;
 					
 				}
 				
 			}
 			
            private function dumpImage(source:Image):void {
            	
            	var asset:* = source.content;
            	var data:BitmapData;
            	var bitmap:Bitmap;
            	
            	try{
            		
            		data = Bitmap(source.content).bitmapData;
                	bitmap = new Bitmap(data);
                	
                	collection.addItem({image:bitmap, label:"item #" + (collection.length + 1)});
            		
            	}catch(error:Error){
            		
            		var loader:Loader = new Loader();
            		
            		loader.contentLoaderInfo.addEventListener(Event.COMPLETE, onBitmapData); 
            		           		
            		var swf:MovieClipLoaderAsset = asset as MovieClipLoaderAsset;            		
            		loader.loadBytes(swf.movieClipData);
            		
            	}
            	
            }
            
            private function onBitmapData(e:Event):void{
            			
            	e.target.removeEventListener(e.type, arguments.callee);
            			
            	var content: MovieClip = MovieClip((e.currentTarget as LoaderInfo).content)
            	var data:BitmapData = new BitmapData(content.width, content.height);
            	data.draw(content, null, null, null, null, true)
            	var bitmap:Bitmap = new Bitmap(data)
            			
            	collection.addItem({image:bitmap, label:"item #" + (collection.length + 1)});
            			
            }
            
        ]]>
    </mx:Script>
 
    <mx:HBox>
        <mx:Panel title="Source image">
            <mx:HBox verticalAlign="middle" horizontalAlign="center" width="100%" height="100%">
                <mx:Image id="img" source="{ARTWORK_PLACE_HOLDER_SWF}" />
            </mx:HBox>
            
            <mx:RadioButtonGroup id="imageSelector" change="handleImage(event)" />
            <mx:RadioButton label="SWF" selected="true" group="{imageSelector}" />
            <mx:RadioButton label="PNG" group="{imageSelector}" />
 
            <mx:ControlBar>
                <mx:Button label="Copy image" click="dumpImage(img)" />
            </mx:ControlBar>
        </mx:Panel>
 
        <mx:TileList id="tileList" dataProvider="{collection}" width="450" height="500" columnCount="4" verticalScrollPolicy="on">
            <mx:itemRenderer>
                <mx:Component>
                    <mx:VBox>
                        <mx:Image source="{data.image}" />
                        <mx:Label text="{data.label}" />
                    </mx:VBox>
                </mx:Component>
            </mx:itemRenderer>
        </mx:TileList>
    </mx:HBox>
 
</mx:Application>

var imageData:BitmapData = BitmapData(someRawBitmapData);
					
var bmp:Bitmap =  new Bitmap(imageData);
					
var matrix:Matrix = new Matrix();
matrix.translate(-((imageData.width - this.width) / 2), -((imageData.height - this.height) / 2));

var matriximage:BitmapData = new BitmapData(bmp.height, bmp.width, false, 0x00000000);
matriximage.draw(bmp, matrix);
					
// Suppose imgThumbnail	is the ID of your component			
imgThumbnail.source = new Bitmap(matriximage);