Upload images from folder with loading gif

<div class="portfolio-modal modal fade" id="portfolioModal1" tabindex="-1" role="dialog" aria-hidden="true">
  <div class="modal-dialog">
    <div class="modal-content">
      <div class="close-modal" data-dismiss="modal">
        <div class="lr">
          <div class="rl"></div>
        </div>
      </div>
      <div class="container">
        <div class="row">
          <div class="col-lg-8 mx-auto">
            <div class="modal-body se-pre-con">
              <!-- Project Details Go Here -->
              <h2 class="">AugenBlick</h2>
               <ul class="ul-li">
                <img src="" alt="">
                  <?php
                    $files = glob("img/Gallery/AugenBlick/*.*");
                    for ($i=1; $i<count($files); $i++)
                    {
                      $num = $files[$i];
                      echo '<li><img class="imggallery lazy" data-src="'.$num.'" alt=""/></li>';
                      }
                  ?>
                  </ul><br>
            </div>
          </div>
        </div>
      </div>
    </div>
  </div>
</div>`

Hello
In the code written above you can see one of six modals of Bootstrap. Using PHP I load all images from a folder into the modal. So that the website doesn’t load forever, the images are only loaded when the modal is open. I want to display a loading gif or something similar in the modal area until the images are loaded. Can someone help me with the code? I have tried many things and found nothing. Thanks

Here the website so you can check the modals
http://riederhslu.bplaced.net/arart/#portfolio

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