var str = "8992";
var begin = "<img src=\"images/contatore/";
var middle = ".jpg\" alt=\"";
var last = "\">";
var nzeri = 6 - str.length;

if (nzeri<=0){
   }
else
if (nzeri>0){
   for(i = 1;i <= nzeri; i++)    {
   document.write(begin + "0" + middle + last);
   }
}

for(x = 0;x < str.length; x++)    {
str1 = str.charAt(x);
document.write(begin + str1 + middle + str1 + last);
}