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(4)); //改成你要随机显示的图片数； 
  if(myNum == 1) document.write("<img src='images/q1.jpg' align='left' hspace='10'><br>"); 
if(myNum == 2) document.write("<img src='images/q2.jpg' align='left' hspace='10'><br>"); //图片路径，可用http:// 
if(myNum == 3) document.write("<img src='images/q3.jpg' align='left' hspace='10'><br>"); 
if(myNum == 4) document.write("<img src='images/q4.jpg' align='left' hspace='10'><br>"); 
else { 
document.write(); 
} 

};