now=new Date() 
sec=(now.getSeconds() )%4
if (sec == 0) 
{img="img/logos/logos_01.gif";
} 
if (sec == 1) 
{img="img/logos/logos_02.gif";
}
if (sec == 2) 
{img="img/logos/logos_03.gif";
} 
if (sec == 3) 
{img="img/logos/logos_04.gif";
} 

document.write("<img src=",img,">");