function StringArray (n) {
  this.length = n;
  for (var i = 0; i < n; i++)
    this[i] = ' '
}
var aantalfotos = 10;

randomImage = new StringArray(aantalfotos);

for (var i = 0; i < aantalfotos; i++)
  randomImage[i] = 'http://www.expatsupport.eu/images/contentright_photo' + (i+1) + '.jpg';

function ranNumber() {
  var ran_unrounded = Math.random()*(randomImage.length-1);
  var ran_number    = Math.round(ran_unrounded);
  return ran_number;
}

function randomimage() {
  if (aantalfotos > 0) document.write("<img src=\"" + randomImage[ranNumber()] + "\" alt=\"\">");
}