if (document.getElementById) { window.onload = swap };
function swap() {
var numimages=7;
rndimg = new Array("http://www.atocarevistaria.com.br/themes/toca/img/bg_header_1.jpg", "http://www.atocarevistaria.com.br/themes/toca/img/bg_header_2.jpg", "http://www.atocarevistaria.com.br/themes/toca/img/bg_header_3.jpg", "http://www.atocarevistaria.com.br/themes/toca/img/bg_header_4.jpg", "http://www.atocarevistaria.com.br/themes/toca/img/bg_header_5.jpg", "http://www.atocarevistaria.com.br/themes/toca/img/bg_header_6.jpg", "http://www.atocarevistaria.com.br/themes/toca/img/bg_header_7.jpg"); 
x=(Math.floor(Math.random()*numimages));
randomimage=(rndimg[x]);
document.getElementById("headerbg").style.backgroundImage = "url("+ randomimage +")"; 
}