script.js

$(function() {
  $('div.content').live('showoff:show', function(evt) {
    var bg_img = $('img[alt=background]', evt.target);
    var old_bg = '';
    if (bg_img.size() > 0) {
      var src = bg_img.attr('src');
      bg_img.hide();
      // Set new background on body
      old_bg = $('body').css('background-image');
      $('body')
        .css('background-image', 'url(' + src + ')')
        .addClass('fullScreen');
    } else {
      $('body').css('background-image', old_bg).removeClass('fullScreen');
    }
  });
});

style.css

body.fullScreen {
    background-repeat: no-repeat;
    background-position: center center;
    background-attachment: fixed;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
}

#preso, .slide {
  border: none !important;
}