var lunchURL = "imgs/lunch1.jpg";

if (document.images) {
     var lunch1 = new Image();
     lunch1.src = "imgs/lunch1.jpg";

     var lunch2 = new Image();
     lunch2.src = "imgs/lunch2.jpg";
	 
	 var lunch3 = new Image();
	 lunch3.src = "imgs/lunch3.jpg";
}

function changeLunch() {
     if (document.images) {
        if (lunchURL == "imgs/lunch1.jpg") lunchURL = "imgs/lunch2.jpg";
		else if (lunchURL == "imgs/lunch2.jpg") lunchURL = "imgs/lunch3.jpg";
		
         document.myLunch.src = lunchURL;
	}
}