var imgNameArray = new Array( 4 );

	imgNameArray[0] = "imgs/main_forrest.jpg";
	imgNameArray[1] = "imgs/main_grape.jpg";
	imgNameArray[2] = "imgs/main_sunflower.jpg";
	imgNameArray[3] = "imgs/main_wave.jpg";

var img = new Image( 700, 250 );
	img.src = imgNameArray[ 0 ];
	
function randomImage()
	{
	var n = Math.round( Math.random() * 3 );
	img.src = imgNameArray[ n ];
	document.images[ "main" ].src = img.src; 
	}