var j=parseInt(Math.random()*2);
  j=(isNaN(j))?0:j;

function writeHomeImage(){
  document.write('<img src="images/photomain'+(j+1)+'.jpg" width="970" height="297" border="0" />');
}

var k=parseInt(Math.random()*1);
  k=(isNaN(k))?0:k;

function writeSubImage(){
  document.write('<img src="images/subphoto'+(k+1)+'.jpg" border="0">');
}

// function to validate input
function checkInput() {
  var missing=focusVal=""
  df=document.forms[arguments[0]]
  arg_num = arguments.length
  j=2
  for(i=1;i<arg_num;i=i+2) {
     current_val = eval("df."+arguments[i]+".value")
     if ( current_val == "" ) {
            missing += "- " + arguments[j] + "\n"
        if ( focusVal=="" ) focusVal = arguments[i]
         }
         j=j+2
  }

  if (missing != "") {
    alert("The following information is required:\n"+missing)
        eval("df."+focusVal+".focus()")

        return false
  }
}