<picture>
  <source srcset="https://assets.codepen.io/210284/1024x800px.png" media="(min-width: 1024px)">
  <source srcset="https://assets.codepen.io/210284/768x600px.png" media="(min-width: 768px)">
  <img src="https://assets.codepen.io/210284/480x375px.png" alt="background">
</picture>

img {
  max-width: 100%;
  display: block; 
  margin: auto;
}