var num=0;

imgArray = [
  ['photo_01.jpg','photo 1 mouseover text','Photo 1'],/*  remember to add comma , at end of line*/
  ['photo_02.jpg','photo 2 mouseover text','Photo 2'],
  ['photo_03.jpg','photo 3 mouseover text','Photo 3'],
  ['photo_04.jpg','photo 4 mouseover text','Photo 4'] /*  no comma , at end of last photo*/
/*  ['photo_05.jpg','photo 5 mouseover text','Photo 5']*/
  ]

function slideshow(slide_num) {
  document.getElementById('mypic').src=imgArray[slide_num][0];
  document.getElementById('mypic').alt=imgArray[slide_num][1];
  document.getElementById('burns').innerHTML=imgArray[slide_num][2];
}

function slideshowUp() {
  num++;
  num = num % imgArray.length;
  slideshow(num);
}

function slideshowBack() {
  num--;
  if (num < 0) {num=imgArray.length-1;}
  num = num % imgArray.length;
  slideshow(num);
}