for (var i=1; i < 15; i++) {
  eval('portraits' + i + '_1 = new Image(80,80)');
  eval('portraits' + i + '_1.src = "images/thumbs/portraits' + i + '_1.jpg"');
  eval('portraits' + i + '_2 = new Image(80,80)');
  eval('portraits' + i + '_2.src = "images/thumbs/portraits' + i + '_2.jpg"');
}