How to change the width and height of an image loaded in a movieclip


I would like to know how I can modify the size properties of an image that is loaded in a movie clip with Loader()
In my example, if I change the width and height properties of the movieclip in which the image is loaded, the image can’t be seen anymore
If I don’t modify the width and height properties, then the image can be seen
What should I modify in my code so that I can change the size properties and still have my image on the scene?

Here is my code

var imgLoader:Loader = new Loader();
var image:URLRequest = new URLRequest('model.jpg');
var imgDisplay:MovieClip = new MovieClip();

// if I change width or height, 
// the image can't be seen, why?
imgDisplay.width = 50;  
imgDisplay.height = 50; 


many thanks for your help