$(function(){
  $("img.o_o").mouseover(function(){
    $(this).attr
    ("src",$(this).attr("src").replace(/^(.+)(\.[a-z]+)$/, "$1_o$2"))
  }).mouseout(function(){
    $(this).attr
    ("src",$(this).attr("src").replace(/^(.+)_o(\.[a-z]+)$/, "$1$2"));
  }).each(function(){
    $("<img>").attr
    ("src",$(this).attr("src").replace(/^(.+)(\.[a-z]+)$/, "$1_o$2"))
  })
})