NumberOfImages = 100;

PartOne = '<a href="img/';
PartTwo = '.jpg"><img src="img/thumbnails/';
PartThree = '.jpg" width="193px" height="140px"></a>';

function printImage() {
  var r = Math.ceil(Math.random() * NumberOfImages);
  document.write(PartOne + r + PartTwo + r + PartThree);
}