$(document).ready(function() {
 $('.ro').hover(function() {
//over
 var newImage = $(this).attr('src').replace(/^(.*?)(\.(?:gif|jpg|png))$/, "$1_o$2");
 $(this).attr('src', newImage);
 },
 function() {
//out
 var newImage = $(this).attr('src').replace('_o', '');
 $(this).attr('src', newImage);
 })
});