rollover
$(function(){
$("img.rollover").mouseover(function(){
$(this).attr("src",$(this).attr("src").replace(/^(.+)(\.[a-z]+)$/, "$1_on$2"));
}).mouseout(function(){
$(this).attr("src",$(this).attr("src").replace(/^(.+)_on(\.[a-z]+)$/, "$1$2"));
});
});
<img class="rollover" src="img_example.jpg" />