$(function(){
  $(".hover").hover(function(){
    var cont = $(this).attr("src");
    cont = cont.replace(/(\.)(jpg|gif|png)/,"_h.$2");
    $(this).attr("src",cont)
  },function(){
    var cont = $(this).attr("src");
    cont = cont.replace(/(_h)\./,".");
    $(this).attr("src",cont)
  });
});