codice:
MovieClip.prototype.alfa = function(immagine){
	this.containerImg.loadMovie(immagine);
	this.containerImg._alpha=0;
        // quando lo fai il preload ?? 
        // this.onEnterFrame=function(){
                car=this.containerImg.getBytesLoaded()
                tot=this.containerImg.getBytesTotal()
                if(car==tot && car>1024){
                   // foto caricata
                   this.containerImg.onEnterFrame=function(){
                        if(this._alpha<99){this._alpha+=5}
                        else{this._alpha=100;delete this.onEnterFrame}
                   }
                 delete this.onEnterFrame
                 }
            }
}
// usare con:

mc.alfa("img/la_casa_del_mare.jpg")