Edit in JSFiddle

<img src="https://placehold.it/600x250" alt="My FPO img" />

<div class="half-container">
  <img src="https://placehold.it/600x250" alt="My FPO img" />
</div>

img {
  max-width: 100%;
  height: auto;
  width: 100%;
}
.half-container {
  width: 50%;
}