function change2(){    document.getElementById("img2").style.zIndex='2';    document.getElementById("img1").style.zIndex='1';    document.getElementById("img1").style.opacity='1';    $("#img2").animate({opacity:'0'},2000);        }function change3(){    document.getElementById("img1").style.zIndex='2';    document.getElementById("img2").style.zIndex='1';    $("#img1").animate({opacity:'0'},2000);    document.getElementById("img2").style.opacity='1';        }function change4(){            setTimeout("change2()",5000);            setTimeout("change3()",12000);            setTimeout("change4()",14000);        } `

通过控制图片的z-index和opacity属性实现图片的交替渐变。