gistfile1.php

<?php

  $headerImageDesktop = get_field('header_image_desktop', 'option');
  $headerImageTablet = get_field('header_image_tablet', 'option');
  $headerImageMobile = get_field('header_image_mobile', 'option');

  if ( $headerImageDesktop && $headerImageTablet && $headerImageMobile ): ?>
        
  <div class="headerConatiner">
    <div class="headerImage">
      <!--  <img id="foo" 
              src="<?php //echo $headerImageDesktop['url']; ?>"
              srcset="<?php //echo $headerImageDesktop['url']; ?> 1024w, <?php //echo $headerImageTablet['url']; ?> 960w, <?php //echo $headerImageMobile['url']; ?> 638w" 
              sizes="100vw"
              alt="" > -->
              
      <picture>
        <!--[if IE 9]><video style="display: none;"><![endif]-->
        <source srcset="<?php echo $headerImageDesktop['url']; ?>" media="(min-width: 960px)">
        <source srcset="<?php echo $headerImageTablet['url']; ?>" media="(min-width: 638px)">
        <img id="foo" srcset="<?php echo $headerImageMobile['url']; ?>" alt="">
        <!--[if IE 9]></video><![endif]-->
      </picture>
              
    </div>
  </div>
  
<?php endif; ?>