我见过一种自动改变图片的特效，请问怎么实现？

试试这个，建议变换时使用滤镜
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
<style type="text/css">
<!--
.text{font-family:Verdana;font-size:18px;color:#fffff0}
#x a:link{font-family:Verdana;font-size:18px;color:#fffff0;text-decoration:none}
#y a:visited{font-family:Verdana;font-size:18px;color:#fffff0;text-decoration:none}
#z a:hover{font-family:Verdana;font-size:18px;color:#00ff00;text-decoration:none}
//-->
</style>
<script language="JavaScript">
<!-- 
intro=new Image();
intro.src='c.gif';                      //默认得图片!              
pics=new Array('a.gif','b.gif','c.gif') //可以放任意个图片，
speed=1000;                                //变幻的速度，单位时毫秒                      load=new Array();
for(i=0; i < pics.length; i++)
 {
 load[i]=new Image();
 load[i].src=pics[i];
 }
ns=(document.layers);
n6=(document.getElementById&&!document.all);
ie=(document.all);
count=-1;
move=1;
chck=null;
timer=null;
vvv='0';
function Picnum(){
var d=(ns||ie)?'document.':'document.getElementById("';
var a=(ns||n6)?'':'all.';
var n6r=(n6)?'")':'';
var p=eval(d+a+'Nums'+n6r);
if (ie||n6)
p.innerHTML='Picture '+count;
if (ns){
 p.document.write("<div style='position:absolute;top:0px;left:0px;font-family:Verdana;font-size:18px;color:#fffff0;text-align:center'>Picture "+count+"</div>");
 p.document.close();
 }
}
function ManualForward(){
 if (chck==1){ 
 count+=move
 if (count >= pics.length) count=0;
 document.images.slides.src=pics[count];
 Picnum();
 }
}
function ManualReverse(){
 if (chck==1){
 count-=move
 if (count < 0) count=pics.length-1;
 document.images.slides.src=pics[count];
 Picnum();
 }
}
function Pause(){
 chck=1;
 count=count;
 clearTimeout(timer)
 Picnum();
}
function AutoCycle(){
 count+=move
 if (count >= pics.length) count=0;
 document.images.slides.src=pics[count];
 Picnum();
 timer=setTimeout('AutoCycle()',speed)
}
function Cycle(){
if (chck==1) AutoCycle();
chck=null;
}
//-->
</script></HEAD><BODY bgcolor=000000 onLoad="setTimeout('AutoCycle()',3000)">
<center>
<table width="250" border="0" cellpadding="0" cellspacing="4">
<tr>
<td valign="middle" align="center" bgcolor="#c0c0c0">
<span class="text" style="position:relative">Slide Show</span>
<br>
<span id="Nums" class="text" style="position:relative">&nbsp;</span>
</td>
</tr>
<tr>
      <td height="250" valign="middle" align="center"> <img src="a.gif" name="slides" width="189" height="189"> 
      </td>
</tr>
<tr>
<td height="40" valign="middle" align="center" bgcolor="#c0c0c0">
<span id="x"><span id="y"><span id="z">
<a href="javascript:ManualReverse()"> << </a>
<a href="javascript:Pause()">暂停</a> 
<a href="javascript:ManualForward()"> >> </a>
<a href="javascript:Cycle()">自动</a> 
</span></span></span>
</td>
</tr>
</table>
</center></BODY>
</HTML>