Markup and styling to fit an image of unknown size into a certain rectangle

image-of-unknown-size.html

<style>
  figure{
    width: /*WIDTH*/;
    height: /*HEIGHT*/;
    overflow: hidden;
    position: relative;
    margin: 0;
    padding: 0;
    float: left;
  }
  figure:before{
    content:'no image';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%,-50%);
    z-index: 0;
  }
  img{
    width: /*ZOOM*/;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%,-50%);
    z-index: 1;
  }
</style>

<figure>
  <img src="...">
</figure>