var imagenumber = 15 ; //Anzahl der Grafiken
var randomnumber = Math.random();
var rand1 = Math.round( (imagenumber-1) * randomnumber) + 1;

images = new Array
images[1] = "/fileadmin/kuota/images/header/kuotaheader1.jpg";
images[2] = "/fileadmin/kuota/images/header/kuotaheader2.jpg";
images[3] = "/fileadmin/kuota/images/header/kuotaheader3.jpg";
images[4] = "/fileadmin/kuota/images/header/kuotaheader4.jpg";
images[5] = "/fileadmin/kuota/images/header/kuotaheader5.jpg";
images[6] = "/fileadmin/kuota/images/header/kuotaheader6.jpg";
images[7] = "/fileadmin/kuota/images/header/kuotaheader7.jpg";
images[8] = "/fileadmin/kuota/images/header/kuotaheader8.jpg";
images[9] = "/fileadmin/kuota/images/header/kuotaheader9.jpg";
images[10] = "/fileadmin/kuota/images/header/kuotaheader10.jpg";
images[11] = "/fileadmin/kuota/images/header/kuotaheader11.jpg";
images[12] = "/fileadmin/kuota/images/header/kuotaheader12.jpg";
images[13] = "/fileadmin/kuota/images/header/kuotaheader13.jpg";
images[14] = "/fileadmin/kuota/images/header/kuotaheader14.jpg";
images[15] = "/fileadmin/kuota/images/header/kuotaheader15.jpg";

var image = images[rand1] 

//document.getElementById("main_menu_container").style.backgroundImage = image;