var imgPath = "/images/pics/";

var numPics = 14;

var lgImg = imgPath+"large-";
var mdImg = imgPath+"medium-";
var smImg = imgPath+"small-";

var lgExt = ".jpg";
var mdExt = ".png";
var smExt = ".png";

function pickImages() {
  lgImg += getRandom()+lgExt;
  mdImg += getRandom()+mdExt;
  smImg += getRandom()+smExt;
  //alert(lgImg+"\n"+mdImg+"\n"+smImg);
}

function getRandom() {
  return Math.floor(Math.random() * numPics + 1);
}

pickImages();