var interval = 2000; //microsecondi

function genArrayIndex(arrLength) {
 arrayIndex=arrLength-Math.floor(Math.random()*arrLength)-1;
 return arrayIndex;
}

function setImage()
{
 var i=0;

 imagelist = new Array();
 imagelist[i] = '2.jpg';
 i++;
 imagelist[i] = '21.jpg';
 i++;
 imagelist[i] = '26.jpg';
 i++;
 imagelist[i] = '3.jpg';
 i++;
 imagelist[i] = '4.jpg';
 i++;
 imagelist[i] = '5.jpg';
 i++;
 imagelist[i] = '7.jpg';
 i++;

 imageIndex=genArrayIndex(imagelist.length);

 return imagelist[imageIndex];
}

function rotateImage() {
 var new_image = setImage();

 window.document.getElementById('rollimage').src='../roll/'+new_image;
 window.document.getElementById('rollanchor').href='dettaglio.asp?art='+new_image;

 var recur_call="rotateImage()";
 setTimeout(recur_call, interval);
}