function clearField(obj, txt) {
  if (obj.value == txt) {
    obj.value = '';
  }
}

function fillField(obj, txt) {
  if (obj.value == '') {
    obj.value = txt;
  }
}

$(document).ready(function(){

  $('#avp').hover(function() {
    $(this).attr("src","images/avp/btn_continue_on.png");
      }, function() {
    $(this).attr("src","images/avp/btn_continue.png");
  });

});