<div class="ppt">
  <a href="###"><img src="ppt/ppt1.jpg" /></a>
  <a href="###" style="display:none;"><img src="ppt/ppt2.jpg" /></a>
  <a href="###" style="display:none;"><img src="ppt/ppt3.jpg" /></a>
  <a href="###" style="display:none;"><img src="ppt/ppt4.jpg" /></a>
  <div class="pptNum">
    <span class="normal">4</span>
    <span class="normal">3</span>
    <span class="normal">2</span>
    <span class="cur">1</span>
  </div>
</div>

/*幻燈片*/
.ppt{ width:270px; height:330px; border:1px solid #ccc; position:relative;}
.ppt img{ position: absolute; top:10px; left:7px; width:255px; height:310px; overflow:hidden;}
.pptNum{ position: absolute; height: 13px; line-height: 14px; bottom:12px; right: 10px; }
.pptNum span{ font-size: 12px; font-weight: 400; color: #FFF; float: right; display: block; width: 24px; text-align: center; background: #000; border-left: solid 1px #FFF; cursor: pointer; }
.pptNum .normal{ color: #FFF; background: #000; filter: Alpha(opacity=50); opacity: .5; }
.pptNum .cur{ background: #ce0609; color: #FFF; }

; (function ($) {
  $.fn.extend({
    "ppting": function (t) {
      var num = 4; //共多少張要輪播的
      var $this = $(this), i = 0, $pics = $('.ppt'), autoChange = function () {
        var $currentPic = $pics.find('a:eq(' + (i + 1 === num ? 0 : i + 1) + ')');
        $currentPic.css({
          display: 'block'
        }).siblings('a').css({
          display: 'none'
        });
        $pics.find('.pptNum>span:contains(' + (i + 2 > num ? num - i : i + 2) + ')').attr('class', 'cur').siblings('span').attr('class', 'normal');
        i = i + 1 === num ? 0 : i + 1;
      }, st = setInterval(autoChange, t || 2000);
      $this.hover(function () {
        clearInterval(st);
      }, function () { st = setInterval(autoChange, t || 2000) });
      $pics.find('.pptNum>span').click(function () {
        i = parseInt($(this).text(), 10) - 2;
        autoChange();
      });
    }
  });
}(jQuery));
$('.ppt').ppting(1000);

<script type="text/javascript" src="js/jquery-1.10.1.min.js"></script>
<script type="text/javascript" src="js/ppt.js"></script>