function ZoomImg(o)
{
var zoom = parseInt(o.style.zoom, 10) || 100;
zoom += event.wheelDelta / 12;
if(zoom > 0)
o.style.zoom = zoom + '%';
return false;
}
{
var zoom = parseInt(o.style.zoom, 10) || 100;
zoom += event.wheelDelta / 12;
if(zoom > 0)
o.style.zoom = zoom + '%';
return false;
}
<img src="images/img.gif" onmousewheel="return ZoomImg(this)" width="200" height="200">