var xPos = 300;
var yPos = 200; 
var step = 1;
var delay = 30; 
var height = 0;
var Hoffset = 0;
var Woffset = 0;
var yon = 0;
var xon = 0;
var pause = true;
var interval;
var imgDom = document.getElementById('img1');
imgDom.style.top = yPos;

function changePos() {
	width = window.screen.availWidth;
	height = window.screen.availHeight;
	Hoffset = imgDom.offsetHeight;
	Woffset = imgDom.offsetWidth;
	imgDom.style.left = xPos + document.body.scrollLeft + "px";
	imgDom.style.top = yPos + document.body.scrollTop + "px";
	if (yon){
		yPos = yPos + step;
	}else{
		yPos = yPos - step;
	};
	if(yPos < 0) {
		yon = 1;
		yPos = 0;
	};
	if (yPos >= (height - Hoffset)){
		yon = 0;
		yPos = (height - Hoffset);
	}
	if (xon){
		xPos = xPos + step;
	}else {
		xPos = xPos - step;
	}
	if (xPos < 0) {
		xon = 1;
		xPos = 0;
	}
	if (xPos >= (width - Woffset)) {
		xon = 0;
		xPos = (width - Woffset);
	}
}
	
function start(){
 	imgDom.visibility = "visible";
	interval = setInterval('changePos()', delay);
}
function pause_resume() {
	if(pause) {
		clearInterval(interval);
		pause = false;
	}else {
		interval = setInterval('changePos()',delay);
		pause = true; 
	}
}
start();