How to create a border for an image that’s been resized with object-fit: scale-down

I have a JavaScript slideshow that displays images of various dimensions in a browser window. It uses object-fit: scale-down to resize the image to fit the container. I’d like to add a border to the image, but when I apply the style border: 2px solid black to the <img> element, it seems to surround what would be the image in its original, unscaled size.

Is there a way, either with CSS or with JavaScript, to apply the border to the resized image?

const duration = 2000; // time (msec) to display each slide
const sizes = [
  [4000, 500],
  [1000, 4000],
  [600, 400],
  [100, 200]
];
const sleep = ms => new Promise(r => setTimeout(r, ms));
let size_index = 0;

function show_slides(duration) {
  let this_duration = duration;
  const my_parent = document.querySelector('#slide-div');
  if (size_index == sizes.length) {
    size_index = 0;
  }
  let w = sizes[size_index][0];
  let h = sizes[size_index][1];
  ++size_index;

  let my_randomizer = `https://placehold.co/${w}x${h}?text=${w}+x+${h}npx`;
  fetch(my_randomizer)
    .then(my_response => my_response.blob())
    .then(my_blob => {
      let my_url = URL.createObjectURL(my_blob);
      sleep(this_duration)
        .then(() => {
          URL.revokeObjectURL(my_parent.querySelector('img').src);
          my_parent.querySelector('img').src = my_url;
          show_slides(duration);
        });
    })
    .catch(my_error => console.error('Error: ', my_error));
}

html {
  height: 100%;
  width: 100%;
}

body {
  /* prevent body from displacing */
  margin: 0;
  /* body should perfectly superimpose the html */
  height: 100%;
  width: 100%;
}

.outer-div {
  display: flex;
  flex-flow: column;
  height: 100%;
  /* Now create left/right margins */
  margin: 0 0.5em;
}

.inner-fixed-div {
  margin-top: 0.5em;
}

.inner-remaining-div {
  margin-bottom: 1em;
  flex-grow: 1;
  /* hints the contents to not overflow */
  overflow: hidden;
}

.picture-div {
  /* force the div to fill the available space */
  width: 100%;
  height: 100%;
}

.picture-div-img {
  /* force the image to stay true to its proportions */
  width: 100%;
  height: 100%;
  /* and force it to behave like needed */
  object-fit: scale-down;
  object-position: center;
  /* does not properly enclose image: */
  border: 2px solid black;
}

<!DOCTYPE html>
<html lang="en">
<!-- Self-contained slideshow demo -->

<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">

</head>

<body onload="show_slides(duration);">
  <div class="outer-div">
    <div class="inner-fixed-div">
      <h1>Lorem Epsom</h1>
    </div>
    <div class="inner-remaining-div">
      <!-- This div will hold the <img> -->
      <div id="slide-div" class="picture-div">
        <!-- Placeholder <img> element for slides -->
        <img class="picture-div-img">
      </div>
    </div>
    <!-- end of inner-remaining-div -->
  </div>
  <!-- end of outer-div -->
</body>

</html>