function getLeaf(url) {
var splited=url.split('?');// remove all the parameter from url
url=splited[0];
return url.substring(url.lastIndexOf("/")+1);// return file name without domain and path
}

jQuery.fn.extend({
 enter: function() {//plugins creation

     return this.each(function() {
       var pth = $(this).find("img")[0];
      //alert($(this).children().attr("href"));
       if($(this).children().attr("href")==getLeaf(document.location.href)){// check that the link url and document url is same
           $(pth).attr("src",pth.src.replace(/.jpg/g, '_on.jpg'));
       } else{
               $(this).hover(function(){
                  $(pth).attr("src",pth.src.replace(/.jpg/g, '_on.jpg'));// mouse over Image
                  },function(){
                      $(pth).attr("src",pth.src.replace(/_on.jpg/g, '.jpg'));// mouse out image
                      });
               }
               });
     }
});