now=new Date() 
sec=(now.getSeconds() )%3
if (sec == 0) 
{img="img/backgrounds/01.jpg";
} 
if (sec == 1) 
{img="img/backgrounds/02.jpg";
} 
if (sec == 2) 
{img="img/backgrounds/03.jpg";
} 
document.write("<img src=",img,">");