/* This function will get the 'name' passed in from the URL.
 * Using further js it can be used to substitute for an image in a web page.
 * Of course if it returns a blank then we can display a default image or error message.
 *
 * In the body section, at the place in question, place a js with document.write... depending 
 * on the return value of the get_field script above.
 */
function get_field(name)
      {
        var rx = RegExp(name + "=([^&]*)");
        var match = document.location.search.match(rx);
        if(!match) return "";
        /* match[0] will be the whole name=value entry, the actual value is in match[1] */
        return match[1];
      }