<div class="w3-section">
    <button class="w3-btn" onclick="plusDivs(-1)"><h6> Prev Image<h6/></button>
    <button class="w3-btn" onclick="plusDivs(1)"><h6>Next Image<h6/> </button><h6/>
  </div>
</div>




<script>
var slideIndex = 1;
showDivs(slideIndex);

function plusDivs(n) {
  showDivs(slideIndex += n);
}

function currentDiv(n) {
  showDivs(slideIndex = n);
}

function showDivs(n) {
  var i;
  var x = document.getElementsByClassName("mySlides");
  var dots = document.getElementsByClassName("demo");
  if (n > x.length) {slideIndex = 1}
  if (n < 1) {slideIndex = x.length}
  for (i = 0; i < x.length; i++) {
     x[i].style.display = "none";
  }
  for (i = 0; i < dots.length; i++) {
     dots[i].className = dots[i].className.replace(" w3-red", "");
  }
  x[slideIndex-1].style.display = "block";
  dots[slideIndex-1].className += " w3-red";
}

window.onload = function() {
    var image = document.getElementById("img");

    function updateImage() {
        image.src = image.src.split("?")[0] + "?" + new Date().getTime();
    }

    setInterval(updateImage, 1000);
}
</script>