$(document).ready(function() {
    $('#download_button a').mousedown(function() {
      $('#download_itrf_image').attr('src', 'images/download_itrf_round_pressed.jpg');
    } );
    $('#download_button a').mouseup(function() {
      $('#download_itrf_image').attr('src', 'images/download_itrf_round_hover.jpg');
    } );
    $('#download_button a').mouseenter(function() {
      $('#download_itrf_image').attr('src', 'images/download_itrf_round_hover.jpg');
    } );
    $('#download_button a').mouseleave(function() {
      $('#download_itrf_image').attr('src', 'images/download_itrf_round.jpg');
    } );
  } );