<img src="foo.jpg" id="parallax1" class="parallax">

<style>
.parallax {
    position : fixed;
    top      : 0px;
    left     : 0px;
}
</style>

<script>
var scroller = $('#parallax1');
$(window).bind('scroll', function(){
   var top = this.scrollTop;
   $('#parallax1').css('top', top * someMultiplier);
});
</script>