CSS position: absolute; and inset: 0; has zero effect on image element

Question

Please see this minimum example:

div {
  position: relative;
  width: 128px;
  height: 128px;
  border: 1px solid red;
}

img {
  position: absolute;
  inset: 0;
}

<div>
  <img src="https://source.unsplash.com/weekly?coffee">
</div>

I thought the image should fill the entire parent box, but the image is overflow, why is this happening?