Problem with event handlers on dynamically loaded images

programming flash
1

Is there a way to get event handlers such as onRollOver to work on dynamically loaded images?

e.g the following code does not work:

createEmptyMovieClip("yes", 20);
loadMovie("images.jpg", "yes");
yes._alpha = 50;
yes.onRollOver = function() {
	this._alpha = 100;
}
yes.onRollOut = function() {
	this._alpha = 50;
}