Ans:

Yes,we can manipulate the image in flex. I think this example will be useful for you.

private var original:BitmapData;
private static const MAX_WIDTH:uint = 1980;
private static var MAX_HEIGHT:uint = 1980;

private function loadImage(url:String):void
{
var requestURL:URLRequest = new URLRequest(url);
var imageLoader:Loader = new Loader();
imageLoader.contentLoaderInfo.addEventListener(Event.COMPLETE, image_Handler);
imageLoader.load(requestURL)
}

private function image_Handler(event:Event):void
{
var bmdImage:BitmapData = Bitmap(event.currentTarget.content).bitmapData;       
var originalWidth:Number = bmdImage.width;
var originalHeight:Number = bmdImage.height;
var newWidth:Number = originalWidth;
var newHeight:Number = originalHeight;  
var matrix:Matrix = new Matrix();   
var scaleX:Number = 1;
var scaleY:Number = 1;

if (originalWidth > MAX_WIDTH || originalHeight > MAX_HEIGHT)
{
sx =  MAX_WIDTH / originalWidth;
sy = MAX_HEIGHT / originalHeight;
var scale:Number = Math.min(sx, sy);
newWidth = originalWidth * scale;
newHeight = originalHeight * scale; 
}
matrix.scale(scale, scale);
original = new BitmapData( newWidth, , newHeight);          
original.draw(bmdImage, matrix);            
}