function hooverEffect(obj){
  obj.style.cursor="hand";
  var i = obj.src.lastIndexOf("/");
  fileName = obj.src.substring(i+1,obj.src.length-4);
  obj.src2 = obj.src.substr(0,i+1)+fileName+"_f2"+obj.src.substr(obj.src.length-4,4);
  obj.src1 = obj.src;
  obj.src = obj.src2;
  obj.onmouseout = function(){this.src=this.src1}
  obj.onmousover = function(){this.src=this.src2}
}