[gorda]

разобралась...

function Image(name, category, year, author){
    this.name = name;
    this.category= category;
    this.year= year;
    this.author= author;
	
	this.addElem = function(group, item){
		for(var key in this){
			if(key==group)	
			{
				
				this[group].push(item);
				alert(this[group]);
			}
		}
	}
	return this;
} ;