// JavaScript Document
//--------------------------------------------------------------------------------------------------------
<!-- Random Image starts-->

<!-- This script and many more are available free online at -->
<!-- The JavaScript Source!! http://javascript.internet.com -->

<!-- Begin
// Set up the image files to be used.
var theImages = new Array() // do not change this
// To add more image files, continue with the
// pattern below, adding to the array.

theImages[0] = 'images-v4/computer-at-desk.jpg'
theImages[1] = 'images-v4/designer-office.jpg'
theImages[2] = 'images-v4/main-with-headphones.jpg'
theImages[3] = 'images-v4/sydney.jpg'
theImages[4] = 'images-v4/designer-office-1.jpg'
theImages[5] = 'images-v4/designer-office-2.jpg'
theImages[6] = 'images-v4/designer-office-3.jpg'
theImages[7] = 'images-v4/designer-office-4.jpg'

// do not edit anything below this line

var j = 0
var p = theImages.length;
var preBuffer = new Array()
for (i = 0; i < p; i++){
   preBuffer[i] = new Image()
   preBuffer[i].src = theImages[i]
}
var whichImage = Math.round(Math.random()*(p-1));
function showImage(){
document.write('<img src="'+theImages[whichImage]+'">');
}

//  End -->
//--------------------------------------------------------------------------------------------------------
<!-- validate form starts -->
function MM_findObj(n, d) { //v4.01
  var p,i,x;  if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
    d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
  if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
  for(i=0;!x&&d.layers&&i<d.layers.length;i++) x=MM_findObj(n,d.layers[i].document);
  if(!x && d.getElementById) x=d.getElementById(n); return x;
}

function MM_validateForm() { //v4.0
  var i,p,q,nm,test,num,min,max,errors='',args=MM_validateForm.arguments;
  for (i=0; i<(args.length-2); i+=3) { test=args[i+2]; val=MM_findObj(args[i]);
    if (val) { nm=val.name; if ((val=val.value)!="") {
      if (test.indexOf('isEmail')!=-1) { p=val.indexOf('@');
        if (p<1 || p==(val.length-1)) errors+='- '+nm+' must contain an e-mail address.\n';
      } else if (test!='R') { num = parseFloat(val);
        if (isNaN(val)) errors+='- '+nm+' must contain a number.\n';
        if (test.indexOf('inRange') != -1) { p=test.indexOf(':');
          min=test.substring(8,p); max=test.substring(p+1);
          if (num<min || max<num) errors+='- '+nm+' must contain a number between '+min+' and '+max+'.\n';
    } } } else if (test.charAt(0) == 'R') errors += '- '+nm+' is required.\n'; }
  } if (errors) alert('Please enter these details:\n'+errors);
  document.MM_returnValue = (errors == '');
}
<!-- validate form ends -->