var ImgNum = 0;
var ImgLength = NewImg.length - 1;

//Time delay between Slides in milliseconds
var delay = 4000;

var lock = false;
var run;

function chgImg(direction) {
if (document.images) {
ImgNum = ImgNum + 1;
if (ImgNum > ImgLength) {
ImgNum = 0;
}
if ( document.getElementById('mainpic') ){
  document.getElementById('mainpic').src = NewImg[ImgNum];
}
}
}

function auto() {
if (lock == true) {
lock = false;
window.clearInterval(run);
}
else if (lock == false) {
lock = true;
run = setInterval("chgImg(1)", delay);
   }
}

 window.onload = function() { auto() ; } ;