How do I load dynamic image assets into adobe air
===

The app I'm working on displays four random images at one point. These four images come from a set of fifty images. If this was a standard Flex project I would just set the img.source property:

    this.img1.source ="../assets/img/"+randomname+".png";`

This isn't working though, I'm getting a broken image. One other way to go about it is to load the image with a urlLoader, which is also not loading the image (unsurprisingly, given that it's a local asset)

    loader = new Loader();
    var urlReq:URLRequest = new URLRequest("../assets/img/"+randomname+".png");
    loader.contentLoaderInfo.addEventListener(Event.COMPLETE, loaded);
    loader.load(urlReq)

So this isn't working either, I'm thinking of loading all of the images into a swc and then linking the swc to the project. This is obviously not great because then all the assets are loaded into memory at runtime. Is there another way of doing this? 

I'm hoping that I'm missing something really simple.

If the .swc solution is the best one, can someone point me in the right direction? I forget how that whole business works, as it's been a couple of years since I've worked with Flex/Flash.  

Thanks in advance 