$(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);
    })
});