// Start which image
function rand(min, max) {
  var offset = min;
  var range = (max - min) + 1;
 
  var randomNumber = Math.floor( Math.random() * range) + offset;
  return randomNumber;
}

var ImageSelect = rand(1,5);	// this specifies the maximum number of IMAGES available

var outputImage = '<td width="280"><img src="images/london/london_' + ImageSelect + '.jpg" width="280" height="500" border="0"></td>';

document.write(outputImage); // output Image
// End which Image