today=new Date();
jran=today.getTime();
function rnd() {
    ia=9301;
    ic=49297;
    im=233280;
    jran = (jran*ia+ic) % im;
    return jran/(im*1.0);
};
function rand(number) {
    return Math.ceil(rnd()*number);
};
for(i=1;i<=1;i++) {
    myNum=(rand(3)); //改成你要随机显示的图片数；
if(myNum == 1) document.write("<img src='/images/banner001.png'>"); 
if(myNum == 2) document.write("<img src='/images/banner002.png'>"); 
if(myNum == 3) document.write("<img src='/images/banner003.png'>"); 
    else {
document.write();
}
};