delete src-attribute with CSS and replace with bg-image

HTML

<img src="http://placedog.com/300/200">
<p>The image-source is deleted with CSS and replaced by a background-image. The original image is a dog :-)</p>

CSS

img {
  content: "";
  background-image: url("http://placekitten.com/300/200");
  width: 300px;
  height: 200px;
  display: inline-block;
}

/* styling basics */

html {
  padding: 20px 0;
  background-color: #efefef;
}

body {
  width: 80%;
  padding: 40px;
  margin: 0 auto;
  background: #fff;
  box-shadow: 1px 1px 5px rgba(0, 0, 0, 0.5);
  font-family: Verdana, Arial, sans-serif;
  font-size: 14px;
}